seismic risk assessment by sidewalk survey and a study on ground supported slab using software...

8/8/2019 SEISMIC RISK ASSESSMENT BY SIDEWALK SURVEY AND A STUDY ON GROUND SUPPORTED SLAB USING SOFTWARE

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SEISMIC RISK ASSESSMENT BY SIDEWALK SURVEYAND

A STUDY ON GROUND SUPPORTED SLAB USINGSOFTWARE STAAD.Pro

SUBMITTED BYMd. Arman Zaman (060203010)Md. Shamsul Arefin Khan (060203014)Prosenjit Paul (060203037)

DEPARTMENT OF CIVIL ENGINEERINGAHSANULLAH UNIVERSITY OF SCIENCE & TECHNOLOGY

141-142 LOVE ROAD, TEJGAON INDUSRIAL AREA, DHAKA 1208

OCTOBER 2010


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SEISMIC RISK ASSESSMENT BY SIDEWALK SURVEYAND

A STUDY ON GROUND SUPPORTED SLAB USINGSOFTWARE STAAD.Pro

SUBMITTED BYMd. Arman Zaman (060203010)Md. Shamsul Arefin Khan (060203014)Prosenjit Paul (060203037)

COURSE: CE-4S0

A THESIS SUBMITTED TO THE DEPARTMENT OF CIVIL ENGINEERING INPARTIAL FULFILLMENT FOR THE DEGREE OF BACHELOR SCIENCE IN CIVIL

ENGINEERINGAHSANULLAH UNIVERSITY OF SCIENCE & TECHNOLOGY

141-142 LOVE ROAD, TEJGAON INDUSTRIAL AREA, DHAKA 1208

OCTOBER 2010


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APPROVED AS TO STYLE AND CONTENT BY

Dr. Md. Mahmudur RahmanAssociate ProfessorDepartment of Civil EngineeringAhsanullah University of science & technology

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TABLE OF CONTENT

LIST OF FIGURELIST OF TABLEACKNOWLEDGMENTABSTRACT

PARTlSEISMIC RISK ASSESSMENT BY SIDEWALK SURVEY

CHAPTER 1INTRODUCTION 2

1 . 1 . 1

1 . 1 . 2

1 . 1 . 3

GeneralStatus of Earthquakes in BangladeshObjective & Scope of Study

368

CHAPTER 2BACKGROUND LITERATURE 9

1 . 2 . 1

1 . 2 . 21 . 2 . 3

IntroductionChronologyReview of previous works

101113

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CHAPTER 3CONCEPT OF EARTHQUAKE ASSESSMENT & METHODOLOGY 1 5

1 . 3 . 1 Introduction 1 61 . 3 . 2 Parameters 1 61 . 3 . 3 Assessment of Available Methods 2 11 . 3 . 4 Statistical Analysis 2 11 . 3 . 5 Variation of building performance with PGV 2 21 . 3 . 6 Intensity dependent expected scores 2 4

CHAPTER 4RESULT 2 6

CHAPTERSCONCLUSION 4 1

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PART-2STRUCTURAL ANALYSIS OF GROUND SUPPORTED SLAB BY STAAD.Pro

CHAPTER 1INTRODUCTION 44

2.1.1 Definition 452.1.2 Installing slabs on ground 462.1.3 Failure of ground supported slabs 462.1.4 Shrinkage and temperature effects 472.1.5 "Difficulties to obtain economical, serviceable concrete floor." 48

CHAPTER 2LITERA TURE REVIEW 52

2.2.1 Introduction 532.2.2 Finite-element method 542.2.3 Construction document information 542.2.4 Slab-on-ground design criteria 552.2.5 Definitions 56

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CHAPTER 3CONCEPT AND METHODOLOGY

2.3.12.3.2

IntroductionMethodology

CHAPTER 4RESUL T AND DISCISSION

2.4.12.4.2

ResultDiscussion

CHAPTERSCONCLUSION

58

5960

63

64118

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Figure No.Figure 1.1.1Figure 1.1.2Figure 1.1.3Figure 1.1.4Figure 1.1.5Figure 1.1.6Figure 1.1.7Figure 1.2.1Figure 1.3.1Figure 1.3.2Figure 1.3.3Figure 1.3.4Figure 1.3.5Figure 2.1.1Figure 2.1.2Figure 2.2.1Figure 2.4.1Figure 2.4.2Figure 2.4.3Figure 2.4.4Figure 2.4.5Figure 2.4.6Figure 2.4.7Figure 2.4.8Figure 2.4.9Figure 2.4.1 0Figure 2.4.11Figure 2.4.12

LIST OF FIGURE

Name of FigureBuildings of Old DhakaBuildings of Old DhakaBuildings of Old DhakaEarthquake zone of BangladeshBuildings of Old DhakaBuildings of Old DhakaBuildings of Old DhakaEarthquake Hazard Zoning Map of Dhaka MegacityBuildings of Old DhakaBuildings of Old DhakaBuildings of Old DhakaSpectral variation of mean plastic deformations in Groups I and N with R.Variation in mean plastic deformation of Group II ground motions for differentRvalues and the first-order polynomial fits.Slab-on-groundCross-Section of Slab-on-groundSlab support system terminologyDisplacement of 15-15 ft slab for comer loadDeflection Curve along edge (outside) of slab (15 -15) due to Comer load + Self-WeightDeflection Curve along very next to edge of slab (15 -15) due to Comer load + Self-WeightDisplacement of 15-15 ft slab for edge loadingDeflection Curve along edge (outside) of slab (15 -15) due to Edge load + Self-WeightDeflection Curve along very next to edge of slab (15 -15) due to Edge loadings + Self-WeightDisplacement of 15-15 ft slab for center loadingDeflection Curve along the nodes next to center of slab (15 -15) due to Comer loadings+ Self-WeightDeflection Curve along the nods next to center of slab (15 -15) due to Comer loadings+ Self-WeightPlate Stress Contour Due To Bending MomentBending Moment Curve along the edge of slab Due to Comer + Self-WeightVariation of Top and Bottom Stress along the edge of slab

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Figure 2.4.13Figure 2.4.14Figure 2.4.15Figure 2.4.16Figure 2.4.17Figure 2.4.18Figure 2.4.19Figure 2.4.20Figure 2.4.21Figure 2.4.22Figure 2.4.23Figure 2.4.24Figure 2.4.25Figure 2.4.26Figure 2.4.27Figure 2.4.28Figure 2.4.29Figure 2.4.30Figure 2.4.31Figure 2.4.32Figure 2.4.33Figure 2.4.34Figure 2.4.35Figure 2.4.36Figure 2.4.37Figure 2.4.38Figure 2.4.39Figure 2.4.40Figure 2.4.41Figure 2.4.42

Plate Stress Contour Due To Bending MomentBending Moment Curve along the edge of slab Due to Edge + Self-WeightVariation of Top and Bottom Stress along the edge of slabPlate Stress Contour Due To Bending MomentBending Moment Curve along the nodes next to the center of slab Due to Comer +Self-WeightVariation of Top and Bottom Stress along the edge of slabDisplacement of 20-20 ft slab for comer loadingDeflection Curve along edge (outside) of slab (20-20) due to Comer loading + Self-WeightDeflection Curve along very next to edge of slab (20-20) due to Comer loading + Self-WeightDisplacement of 20-20 ft slab for edge loadingDeflection Curve along edge (outside) of slab (20-20) due to Edge loading + Self-WeightDeflection Curve along very next to edge of slab (20-20) due to Edge loadings + Self-WeightDisplacement of 20-20 ft slab for center loadingDeflection Curve along the nodes next to center of slab (20-20) due to Comer loadings+ Self-WeightDeflection Curve along the nods next to center of slab (20-20) due to Comer loadings+ Self-WeightPlate Stress Contour Due To Bending MomentBending Moment Curve along the edge of slab Due to Comer + Self-WeightVariation of Top and Bottom Stress along the edge of slabPlate Stress Contour Due To Bending MomentBending Moment Curve along the edge of slab Due to Edge + Self-WeightVariation of Top and Bottom Stress along the edge of slabPlate Stress Contour Due To Bending MomentBending Moment Curve along the nodes next to the center of slab Due to Comer +Self-WeightVariation of Top and Bottom Stress along the edge of slabDisplacement of25-25 ft slab for comer loadingDeflection Curve along edge (outside) of slab (25-25) due to Comer loading + Self-WeightDeflection Curve along very next to edge of slab (25-25) due to Comer loading + Self-WeightDisplacement of 25-25 ft slab for edge loadingDeflection Curve along edge (outside) of slab (25-25) due to Edge loading + Self-WeightDeflection Curve along very next to edge of slab (25-25) due to Edge loadings + Self-Weight

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Figure 2.4.43Figure 2.4.44Figure 2.4.45

Figure 2.4.46Figure 2.4.47Figure 2.4.48Figure 2.4.49Figure 2.4.50Figure 2.4.51Figure 2.4.52Figure 2.4.53Figure 2.4.54

Displacement of 25-25 ft slab for center loadingDeflection Curve along the nodes next to center of slab (25-25) due to Comer loadings+ Self-WeightDeflection Curve along the nods next to center of slab (25 -25) due to Comer loadings+ Self-WeightPlate Stress Contour Due To Bending MomentBending Moment Curve along the edge of slab Due to Comer + Self-WeightVariation of Top and Bottom Stress along the edge of slabPlate Stress Contour Due To Bending MomentBending Moment Curve along the edge of slab Due to Edge + Self-WeightVariation of Top and Bottom Stress along the edge of slabPlate Stress Contour Due To Bending MomentBending Moment Curve along the nodes next to the center of slab Due to Comer +Self-WeightVariation of Top and Bottom Stress along the edge of slab

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Table No.Table 1.2.1Table 1.3.1Table 1.3.2Table 1.3.3Table 1.4.1Table 1.4.2Table 1.4.3Table 1.4.4Table 1.4.5Table 1.4.6Table 1.4.7Table 1.4.8Table 1.4.9Table 2.1.1Table 2.1.2Table 2.1.3Table 2.4.1Table 2.4.2Table 2.4.3Table 2.4.4Table 2.4.5Table 2.4.6Table 2.4.7Table 2.4.8Table 2.4.9Table 2.4.10Table 2.4.11Table 2.4.12Table 2.4.13Table 2.4.14Table 2.4.15Table 2.4.16Table 2.4.17Table 2.4.18

List of Tables

Name of TableChronology of important earthquakes from 1548Observed Performance scoreCalculated performance-modification factorsInitial performance scoresThe value of the coefficientCalculated EPS value and comment (Buet Teachers Quarter)Calculated EPS value and comment (Buet Staff Quarter)Calculated EPS value and comment (Bakshi Bazar - Urdu Road)Calculated EPS value and comment (Khaja Dayan 1st Lane)Calculated EPS value and comment (Chalk Bazar Azgor Lane)Calculated EPS value and comment (Hosni Dalan)Calculated EPS value and comment (Ajimpur Colony)Calculated EPS value and comment (Hori Dash Lane)Cracking Of the SlabDamp or wet floor slab, excessive humidityCold floorsNode displacement (15-15) for Comer + SelfweightNode displacement (15-15) for Edge + Self WeightNode displacement (15-15) for Center + Self WeightPlate Centre Principal Stresses and Bending Moment for Comer + Self weight (15 -15)Plate Centre Principal Stresses and Bending Moment Edge + Self Weight (15-15)Plate Centre Principal Stresses and Bending Moment Center + Self Weight (15-15)Node displacement (20-20) for Comer + SelfweightNode displacement (20-20) for Edge + Self WeightNode displacement (20-20) for Center + Self WeightPlate Centre Principal Stresses and Bending Moment for Comer + Self weight (20-20)Plate Centre Principal Stresses and Bending Moment Edge + Self Weight (20-20)Plate Centre Principal Stresses and Bending Moment Center + Self Weight (20-20)Node displacement (25-25) for Comer + SelfweightNode displacement (25-25) for Edge + Self WeightNode displacement (25-25) for Center + Self WeightPlate Centre Principal Stresses and Bending Moment for Comer + Self weight (25 -25)Plate Centre Principal Stresses and Bending Moment Edge + Self Weight (25-25)Plate Centre Principal Stresses and Bending Moment Center + Self Weight (25-25)

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ACKNOWLEDGMENT

We desire to express our heartiest gratitude to Dr. Md. Mahmudur Rahman, AssistantProfessor, Department of Civil Engineering of Ahsanullah University of Science andTechnology and Supervisor of this Thesis. We faced many problems while going through thisassignment. We should also express our convivial gratitude to him, for all support andencouragement. He also guided us all the way and helped us to accomplish our aspiration. Hisunstinting efforts on our behalf are worth mentioning. We are certainly indebted for his preciousinsights. Those proved more than enough to overcome the difficulties.

The authors would like to express deep regards to Professor Dr. Abdul Halim, Head ofDepartment of Civil Engineering, and AUST for providing a nice environment and for helping tocomplete this research work.

We politely remember Late Prof. Dr. A. M. Shadulla for his encouragement and supportin completing the work.

We also express our regards and warm gratefulness to all of our teachers of AhsanullahUniversity of Science and Technology, for their valuable advice and facilitate.

We would like to acknowledge and thank our parents, too who helped us to learn weknew nothing.

At last, we affectionately appreciate all of friends for their cordial helps thorough out theyear.

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Abstract

The research study performed here aims at estimation of vulnerability of urban buildingsunder seismic load during earthquake. The vulnerability is estimated by calculating aperformance score for building by a method called "Sidewalk Survey". The method followedhere is according to the screening method developed by the Middle East Technical University,Turkey. It is an effective step for seismic risk mitigation in large urban areas.

This survey aims a fast and simple seismic risk assessment procedure for vulnerablebuildings. The procedure is based on observing selected buildings' parameters such as soft story,overhangs, building qualities, presence of short columns etc. from street side and estimatingexpected performance score known as EPS.

This "Estimated Performance Score" (EPS) denotes the vulnerability of buildings duringearthquake. The identification of such buildings by evaluating their EPS value can reduce theseismic risk either by retrofitting or by replacing those buildings, the hazards of earthquake canbe minimized.

Most of the existing evaluation methods refer to a single building, rather than a wholearea. However, this method of sidewalk survey estimates the earthquake risk assessment for thebuildings of a given area. The reliability of these methods differ considerably, from limitedreliability of the simple statistical and rapid screening methods, to the most reliable methods thatare based on detailed analytical procedures that may evaluate the mechanical behavior of thestructural system under consideration, but require an enormous amount of data, that is commonlynot available, and take much time in their processing.

Here the survey is done in the area of "Old Dhaka". The method of Sidewalk Survey isfollowed here. The survey is a visual observation of the parameters of the buildings from theroadside. A peak ground velocity (PGV) value for this area is chosen. Then the value of EPS iscalculated using various vulnerability co-efficient.

The thesis paper also includes another study, which is concerned with the analysis ofbehavior of the slab on grade under various loading condition. Here concentrated loads on theslab at three different positions are taken into account. The positions considered are - at thecentre, at the comer and at the edge of the slab. The analysis is done by using the software-STAAD.Pro.

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The thesis aims to graphical analysis the behavior of the slab. The graphs are constructedwith the results for different loading condition, obtained from the analysis by STAAD.Pro. Thegraph shows the critical point of a slab for a specific loading as well as the other pointsrespectively.Failures of concrete slab on grade are frequent. Cracks may be caused from unequal settlement.The critical point on the graph shows the most vulnerable location for loadings. This thesis studytreats these points and analyzes the behavior of the slab.

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PART -1SEISMIC RISK ASSESSMENT BY SIDEWALK SURVEY

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CHAPTERlINTRODUCTION

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1.1.1 GeneralEarthquakes originate due to various reasons, which fall into two major categories viz

non-tectonic and tectonic. The origin of tectonic earthquakes is explained with the help of'elastic rebound theory'. Earthquakes are distributed unevenly on the globe. However, it hasbeen observed that most of the destructive earthquakes originate within two well-definedzones or belts namely, 'the circum-Pacific belt' and 'the Mediterranean-Himalayan seismic belt'.

Although Bangladesh is extremely vulnerable to seismic activity, the nature and the levelof this activity is yet to be defined. In Bangladesh, complete earthquake monitoring facilities arenot available. The Meteorological Department of Bangladesh established a seismic observatoryat Chittagong in 1954. This remains the only observatory in the country.

The classical engineering approach for providing seismic safety in building structures isto ensure their conformance to the current seismic design codes. This is indeed a valid approachfor new buildings. However, the majority of the existing buildings in seismic regions do notsatisfy modem code requirements. Yet, the ratio of severely dam- aged or collapsed buildingsobserved after a severe earthquake is much less than the ratio of substandard buildings. Thedifference is usually significant.

An effective step for seismic risk mitigation in large urban areas under high seismic riskis to identify the most vulnerable buildings that may sustain significant damage during a futureearthquake. Once they are identified properly, existing seismic risks may be reduced either byretrofitting such buildings, or by replacing them with new buildings in view of a particular risk-mitigation planning strategy.

It is basically a sidewalk survey procedure based on observing selected buildingparameters from the street side, and calculating a performance s core for determining therisk priorities for buildings.

Several studies have been made on buildings of Dhaka City. Most of its residentialbuildings, as is quite typical all over Dhaka, were built during the last 100 years. There are some5000 low to moderate height (up to 2-8 stories) residential buildings in Old Dhaka. In the firststage of the research, a group of buildings was arbitrarily selected in order to implement themethodology's procedures and then conduct site visits in order to document and compare the realdata with the predicted data. Comparisons were done between the estimated values establishedaccording to the present methodology and the real values of the examined buildings. The

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following parameters were compared: the number of dwelling units per typical floor, the numberof expansion joints and the number of stories in the building. The comparison shows goodpredictions, with a limited number of discrepancies, which are related to several reasons amongwhich are:

Figure: 1.1.1 Building of Old Dhaka

uncommon distance between expansion joints in one building, mistaken data in the basicGIS database regarding the height of the building in another building, and in another building wefound out that retrofit of the building was carried out long after its construction and added a newwing thus adding significantly to the dwelling unit area. These discrepancies cannot be predicted,however they are exceptional compared to a very good correspondence of all other examinedbuildings.

There are various methods followed for estimating the seismic risk. The sidewalk surveyis the most relative for this research. The buildings of Old Dhaka are examined by visualobservation, which includes observation of the parameters like as soft storey, heavy overhangsand apparent building quality.

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Figure: 1.1.2 Building of Old DhakaThere are various methods followed for estimating the seismic risk. The sidewalk survey

is the most relative for this research. The buildings of Old Dhaka are examined by visualobservation, which includes observation of the parameters like as soft storey, heavy overhangsand apparent building quality.


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Figure: 1.1.6 Building of Old DhakaIn the zoning map, Bangladesh has been divided into three generalized seismic zones:

zone-zone-II, zone-III and I. Zone-I compressing the northern and eastern regions ofBangladesh with the presence of the Dauki Fault system of eastern Sylhet and the deepseated Sylhet Fault, and proximity to the highly disturbed southeastern Assam region with

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the Jaflong thrust, Naga thrust and Disang thrust, is a zone of high seismic risk with a basicseismic co-efficient of 0.08. Northern Bangladesh comprising greater Rangpur and Dinajpurdistricts is also a region of high seismicity because of the presence of the Jamuna Fault and theproximity to the active east-west running fault and the Main Boundary Fault to the north in India.The Chittagong- Tripura Folded Belt experiences frequent earthquakes, as just to its east is theBurmese Arc where a large number of shallow depth earthquakes originate. Zone-II comprisingthe central part of Bangladesh represents the regions of recent uplifted Pleistocene blocks of theBarind and Madhupur Tracts, and the western extension of the folded belt. The Zone-IIIcomprising the southwestern part of Bangladesh is seismically quiet, with an estimated basicseismic co-efficient of 0.04.

1.1.3 Objective& Scope of StudyThe scopes are expanding, fragility functions pertain to a group of buildings in the whole

area of Old Dhaka rather than a specific building. The scope of the study presented hereinextends one-step further: several selected parameters are evaluated simultaneously to obtain aperformance score for each building. This score separates each building from the other buildingsin the inventory in risk classification. As a result, the vulnerability of a building is identified. Amitigation of earthquake risk or damages is possible then. The study is a prediction of thevulnerable buildings.


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CHAPTER 2BACKGROUND LITERATURE

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CHAPTER 2BACKGROUND LITERATURE

1.2.1 IntroductionEarthquake is trembling or shaking movement of the earth's surface. Most earthquakes

are minor tremors, while larger earthquakes usually begin with slight tremors, rapidly take theform of one or more violent shocks, and end in vibrations of gradually diminishing forcecalled aftershocks. Earthquake is a form of energy of wave motion, which originates in alimited region and then spreads out in all directions from the source of disturbance. Itusually lasts for a few seconds to a minute. The point within the earth where earthquakewaves originate is called the focus, from where the vibrations spread in all directions.They reach the surface first at the point immediately above the focus and this point is called theepicenter. It is at the epicenter where the shock of the earthquake is first experienced. Based onthe depth of focus, an earthquake may be termed as shallow focus (0-70 km), intermediate focus(70-300 km), and deep focus (> 300 km). The most common measure of earthquake size is theRichter's magnitude (M). The Richter scale uses the maximum surface wave amplitude inthe seismogram and the difference in the arrival times of primary (P) and secondary (S)waves for determining magnitude (M). The magnitude is related to roughly logarithm ofenergy, E in ergs.

Accurate historical information on earthquakes is very important III evaluating theseismicity of Bangladesh in close coincidences with the geotectonic elements. Information onearthquakes in and around Bangladesh is available for the last 250 years. The earthquakerecord suggests that since 1900 more than 100 moderate to large earthquakes occurred inBangladesh, out of which more than 65 events occurred after 1960. This brings to lightan increased frequency of earthquakes in the last 30 years. This increase in earthquakeactivity is an indication of fresh tectonic activity or propagation of fractures from the adjacentSEISMIC Zones.

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1.2.2 ChronologyBefore the coming of the Europeans, there was no definite record of earthquakes.

Following is a chronology of important earthquakes from 1548.

Table 1.2.1 Chronology of important earthquakes from 15481548 The first recorded earthquake was a terrible one. Sylhet and Chittagong were violently

Shaken, the earth opened in many places and threw up water and mud of a sulphuroussmell.

1642 More severe damage occurred in Sylhet district. Buildings were cracked but there was noLoss of life.

1663 Severe earthquake in ASSAM, which continued for half an hour and Sylhet district wasnot free from its shock.1762 The great earthquake of April 2, which raised the coast of Foul island by 2.74m and thenorthwest coast ofChedua island by 6.71m above sea level and also caused a permanentsubmergence of 155.40 sq km near Chittagong. The earthquake proved very violent inDhaka and along the eastern bank of the MEGHNA as far as Chittagong. In Dhaka 500persons lost their lives, the Rivers and JHEELs were agitated and raised high above theirusual levels and when they receded, their banks were strewn with dead fish. A large riverdried up, a tract of land sank and 200 people with all their CATTLE were lost. Twovolcanoes were said to have opened in the Sitakunda hills.

1775 Severe earthquake in Dhaka around April 10, but no loss of life.1812 Severe earthquake in many places of Bangladesh around May 11. The earthquakeproved violent in Sylhet.1865 Terrible shock was felt, during the second earthquake occurred in the winter of 1865,

although no serious damage occurred.1869 Known as Cachar Earthquake. Severely felt in Sylhet but no loss of life. The steeple ofthe church was shattered, the walls of the courthouse and the circuit bungalow crackedand in the eastern Dart of the district the banks of manv rivers caved in.1885 Known as the Bengal Earthquake. Occurred on 14 July with 7.0 magnitude and theepicenter was at Manikganj. This event was generally associated with the deep-seatedJamuna Fault.1889 Occurred on 10 January with 7.5 magnitudes and the epicenter at Jaintia Hills. It affectedSylhet town and surrounding areas.

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1897 Known as the Great India Earthquake with a magnitude of8.7 and epicenter at ShillongPlateau. The great earthquake occurred on 12 June at 5.15 pm, caused serious damage tomasonry buildings in Sylhet town where the death toll rose to 545. This was due to thecollapse of the masonry buildings. The tremor was felt throughout Bengal, from thesouth Lushai Hills on the east to Shahbad on the west. In Mymensingh, many publicbuildings of the district town, including the Justice House, were wrecked and very few ofthe two-storied brick-built houses belonging to ZAMINDARs survived. Heavy damagewas done to the bridges on the Dhaka-Mymensingh railway and traffic was suspendedfor about a fortnight. The river communication of the district was seriously affected(BRAHMAPUTRA). Loss of life was not great, but loss of property was estimated atfive million Rupees. Rajshahi suffered severe shocks, especially on the eastern side, and15 persons died. In Dhaka, damage to property was heavy. In Tippera, masonry buildingsand old temples suffered a lot and the total damage was estimated at Rs 9,000.

1918 Known as the Srimangal Earthquake. Occurred on 18 July with a magnitude of 7.6 andepicenter at Srimangal, Maulvi Bazar. Intense damage occurred in Srimangal, but inDhaka only minor effects were observed.

1930 Known as the Dhubri Earthquake. Occurred on 3 July with a magnitude of 7.1 and theepicenter at Dhubri, Assam. The earthquake caused major damage in the eastern parts ofRanznur district.1934 Known as the Bihar-Nepal Earthquake. Occurred on 15 January with a magnitude of 8.3and the epicenter at Darbhanga of Bihar, India. The earthquake caused great damage inBihar Nepal and Uttar Pradesh but did not affect any part of Bangladesh.Another earthquake occurred on 3 July with a magnitude of 7.1 and the epicenter aDhubri of Assam, India. The earthquake caused considerable damages in greaterRangpur district of Bangladesh.1950 Known as the Assam Earthquake. Occurred on 15 August with a magnitude of 8.4 withthe epicenter in Assam, India. The tremor was felt throughout Bangladesh but no damagewas reported.

1997 Occurred on 22 November in Chittagong with a magnitude of 6.0. It caused minordamage around Chittagong town.

1999 Occurred on 22 July at Maheshkhali Island with the epicenter in the same place, amagnitude of 5.2. Severely felt around Maheshkhali island and the adjoining ~Houses cracked and in some cases collapsed.

2003 Occurred on 27 July at Kolabunia union of Barkal upazila, Rangamati district withmagnitude 5.1. The time was at 05:17:26.8 hours.

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1.2.3 Review of previous worksSaidur Rahman (Director of Bangladesh Disaster Preparedness Centre)

A world famous seismologist Professor Billham said in 2001 that in the Himalayanregion, at least seven earthquakes of the strength 8.1 and above on the Richter scale are overdue.A team of experts led by him did a survey, they identified seven to eight risk prone countries,and Bangladesh is obviously one of them because of its geographical location. Secondly, a studyby a UN sponsored program called International Decade for Natural Disaster Reduction in theperiod from 1991 till 2000 surveyed at least 30 different cities. In addition, the findings of thesurvey are very threatening to us. They are saying that the two most vulnerable cities toearthquake are Tehran and Dhaka. There were several factors to come to this conclusion. Forexample situation in an earthquake zone, physical infrastructure, socio-economic condition of thepeople living there and most importantly response management.

Dr M Shahidul Islam (Professor, Department of Geography, University of Chittagong)Potential earthquake threat and our coping strategies

Although earthquake in Bangladesh has not yet been recognized as a case of senousnatural disaster, but recent occurrences and assumptions have already generated a potentialthreat. The incidents of recent repeated earthquakes on 27 July in Chittagong have raised a greatconcern among the people of the country, particularly among those around Chittagong region.

Geographically Bangladesh is located close to the boundary of two active plates: theIndian plate in the west and the Eurasian plate in the east and north. As a result, the country isalways under a potential threat of earthquake of any magnitude at any time, which might causecatastrophic devastation in less than a minute. In the seismic zoning map of Bangladesh,Chittagong region has been shown under Zone II with basic seismic coefficient of 0.05, butrecent repeated jerk around this region indicate the possibilities of potential threat of even muchhigher intensity than projected.

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Figure 1.2.1: Earthquake Hazard Zoning Map of Dhaka Megacity

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CHAPTER 3CONCEPT OF EARTHQUAKE ASSESSMENT &

METHODOLOGY

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CHAPTER 3CONCEPT OF EARTHQUAKE ASSESSMENT &

METHODOLOGY

1.3.1 IntroductionRecent earthquakes in urban environments revealed that building damage increases with

the number of stories when the building lacks basic seismic-resistant design features. Otherfactors that have significant contribution to damage are also well established. These are thepresence of severe irregularities such as soft stories and heavy overhangs; other discontinuities inload paths; poor material quality, detailing, and workmanship. It is usually difficult to quantifythe sensitivity of damage to each parameter analytically; however, statistics help. Fragilityfunctions may be developed for determining damage probabilities, hence for estimating losses incertain building types under given ground-motion intensities.

The proposed approach aims at developing of a rapid GIS based technique for assessingthe structural systems of a large inventory of residential buildings, where only limited data isavailable. There is need for much more data in order to come up with the "most likely" structuralscheme of a building that will enable its analysis, and this data is derived from logical proceduresthat are based on several databases. The proposed methodology makes an attempt to produce theinformation from a "distance", namely without the need to search for the buildings documents, orconduct site visits to check and document the buildings, or perform any measurements or testswhatsoever. The entire work is done in the office by a computerized set of algorithms, withautomatic decisions based on pre-defined rules, at a very short time and with minimal timeresources compared to all other alternatives.

1.3.2 ParametersSome of the important stated parameters that influence damage significantly can be

determined quite easily by visual observation. The simplest ones are the number of stories, softstories, heavy overhangs, and the overall apparent quality of the building reflecting the quality ofconstruction. These are discussed separately below

Number of stories Presence of soft story Presence of heavy overhangs Apparent building quality

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Presence of short columns Pounding between adjacent buildings Local soil conditions Topographic effects

1.3.2.1 Number of StoriesField observations of earthquakes revealed a very significant correlation between the

number of unrestrained stories and the severity of building damage. If all buildings conformed tomodem seismic design codes, then such a distribution would not occur and a uniformdistribution of damage would be expected regardless of the number of stories. The increase inseismic demand with the number of stories is not balanced with the increase in seismic capacityin substandard buildings.

Figure: 1.3.1 A High Storied Building of Old Dhaka

It can be observed that damage grades shift almost linearly with the number of stories.However, the objectivity of the assigned damage grades is questionable since the distributions

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indicate higher damage than that observed by the field survey teams deployed by the Middle EastTechnical University. Particularly, assignment of moderate and higher damage grades to all five-and six-story buildings is misleading. The number of freestanding stories in a building isidentified as the number of "seismic" stories in this study. The number of stories is counted on anobservational basis.


1.3.2.2 Presence of a Soft StorySoft stories usually exist in buildings when the ground story has less stiffness and

strength compared to upper stories. This situation mostly arises in buildings located along theside of a main street. Ground stories that have level access from the street are reserved ascommercial space whereas residences occupy the upper stories. These upper stories benefit fromthe additional stiffness and strength provided by many partition walls, but the commercial spaceat the bottom is mostly left open between the frame members for customer circulation. Besides,the ground stories may have taller clearances and different axis systems, causing furtherirregularity. The compound effect of all these negative features from the earthquake-engineeringperspective is identified as a soft story.

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Figure: 1.3.3 Buildings of Old Dhaka

During street surveys, the presence of a soft story is evaluated on an observational basis,where the answer is either yes or no.

1.3.2.3 Presence of Heavy OverhangsHeavy balconies and overhanging floors in multistory reinforced concrete buildings shift

the mass center upwards; accordingly increase seismic lateral forces and overturning momentsduring earthquakes. Buildings having balconies with large overhanging cantilever spans enclosedwith heavy concrete parapets sustained heavier damages during earthquakes compared to regularbuildings in elevation. Since this building feature can easily be observed during the SidewalkSurvey, it is included in the parameter set.

1.3.2.4 Apparent Building QualityThe material and workmanship quality, and the care given to its maintenance reflect the

apparent quality of a building. The buildings apparent quality roughly observed as good,moderate or poor. A close relationship had been observed between the apparent quality and

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experienced damage during the recent earthquakes. A building with poor apparent quality can beexpected to possess weak material strengths and inadequate detailing.1.3.2.5 Presence of Short Columns

Semi-in filled frames, band windows at the semi-buried basements or mid-story beamsaround stairway shafts lead to the formation of short columns in concrete buildings. Thesecaptive columns usually sustain heavy damage during strong earthquakes since they are notoriginally designed to receive the high shear forces relevant to their shortened lengths. Shortcolumns can be identified from outside because they usually form along the exterior axes.

1.3.2.6 Pounding between Adjacent BuildingsWhen there is no sufficient clearance between adjacent buildings, they pound each other

during an earthquake as a result of different vibration periods and consequent non -synchronizedvibration amplitudes. Uneven floor levels aggravate the effect of pounding. Buildings subjectedto pounding receive heavier damages at the higher stories.

1.3.2.7 Local Soil ConditionsSite amplification is one of the major factors that increase the intensity of ground

motions. Although it is difficult to obtain precise data during a street survey, an expert observercan be able to classify the local soils as stiff or soft. In urban environments, geotechnical dataprovided by local authorities is a reliable source for classifying the local soil conditions.

1.3.2.8 Topographic EffectsTopographic amplification IS another factor that may increase the ground motion

intensity on top of hills. Besides, buildings located on steep slopes (steeper than 30 degrees)usually have stopped foundations, which are incapable of distributing the ground distortionsevenly to structural members above. Therefore, these two factors must be taken into account inseismic risk assessment. Both factors can be observed easily during a street survey.

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1.3.3 Assessment of Available MethodsMost of the existing evaluation methods refer to a single building, among which we may

find: methods that a rebased on statistics of past EQ damage records (Whitman, 1974), methodsthat are based on experts subjective opinion (ATC-13, 1985. FEMA 178, 1992. EMS 1998)methods that are based on score assignments of predefined checklists exposing structuraldeficiencies that do not contain even elementary engineering calculations (FEMA 154/5, 1998.NRC-CNRC, 1996. NZSEE, 1996. 1 . S 2413, 2003), simple analytical methods to simulatebuildings response that are essentially simple approximate solutions that must rely on a fewparameters (ATC-14, 1987. Calvi, 1999. Priestley, 2003) and detailed analytical procedures(ASCE 41-06, 2007) which are more accurate but require much data and are time-consuming.

The reliability of these methods differ considerably, from limited reliability of the simplestatistical and rapid screening methods, to the most reliable methods that are based on detailedanalytical procedures that may evaluate the mechanical behavior of the structural system underconsideration, but require an enormous amount of data, that is commonly not available, and takemuch time in their processing.

The Sidewalk Survey differs from these methods. It requires few parameters. Theseparameters can be observed from the exterior side of the buildings. Specially four parametersincludes soft storey, heavy overhangs, no. of stories, apparent quality are used in this survey. Thevulnerability of buildings is identified by a performance score. The EPS value is estimated froma mathematical relation between the parameters, vulnerability co -efficient and the PGV value.The PGV value is specially chosen for the survey area Old Dhaka. This EPS value estimates thevulnerability of buildings for earthquake.

1.3.4 Statistical AnalysisThe objective of statistical analysis is to develop a performance score for prioritizing the

buildings in an urban area, based on a set of vulnerability indicators that can be observed visuallythrough a street survey. Multiple linear regression analysis is employed for developing a mean-value function that returns the expected value of the performance score.

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1.3.5 Variation of Building Performance with PGVThe seismic performance of a structure subjected to severe ground motion can be

measured by the observed structural damage. The maximum post-yield deformation (plasticdeformation) experienced by a structure during severe earthquake ground motion can beaccepted as one of the major contributors to structural damage. Hence, it can be accepted as asuitable performance parameter in quantifying the damage, as it is zero when the structurebehaves in its elastic limits and takes larger values as the structure deforms beyond its yieldinglevel.

Nonlinear response history analyses of SDOF systems are performed using the strongground-motion data described in the preceding section. The inelastic behavior is simulated by theelastoplastic hysteretic model. At a given period of vibration, the maximum plastic deformation,Ap, of an SDOF system is computed for a lateral elastic strength demand that is normalized bythe corresponding lateral yield strength value.

E[Llp[(cm)70 ,-------------------------,

20 ,mil < PGV < 40 emf!

50

-R=6,Q

-R1,S60 -R=l.O

--R=3,Q_.-R=4.0

40 R=S,Q

3020

0.0 0.5 1.0 1- 5 20~1I10!1 [& )

2.S

E{~p](~m)70,-------------------------,PGV ~ BOtmfl

20)0

-R=j.~60 -R"l.O

-R=3.Q50 -R"4.Q40 -R=5.Q-R"lill

10

O~~~--~--~----~--~--~3.0 0.0 0.5 1.0 1.5 2.0P9~cd [1 1

2.5 3.0

Figure: 1.3.4 Spectral variation of mean plastic deformations in Groups I and IV with R.

This normalized lateral strength parameter is known as the strength reduction factor R.The maximum plastic SDOF deformations computed in this way correspond to plasticdeformation spectra for constant strength. A total of six R values (1.5, 2.0, 3.0, 4.0, 5.0, and 6.0)are used in these computations.

Figure 1.3.4 presents the variation in mean ~p values with respect to the period ofvibration and R factor for ground-motion data Groups I and IV. Comparison of curves forGroups I and IV indicates the sensitivity of plastic deformations to PGV. The curves inFigure1.3.4 also show the changes in mean plastic deformation trend with respect to the strengthreduction factor R. The mean plastic deformation values obtained for the ground motions withlarger PGV exhibit a stronger sensitivity to the R factor.

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Figure 1.3.5 shows a close-up view of mean plastic deformation variation in Group IIground motions for periods of vibration between 0.1 and 1.0 s. The mean plastic deformationvalues follow an almost well defined, linear trend with respect to the R factors. The first-orderpolynomial fits computed for each R value are also shown in Figure 1.3.5. Similar to the fitspresented in Figure 1.3.5, mean plastic deformation curves of other ground-motion groups arerepresented by linear straight lines for periods of vibration between 0.1 and 1.0 s, and these fitsyielded very high correlation coefficients with respect to the actual data trend. It should be notedthat the period interval from 0.1 to 1.0 s contains a significantly large percentage of existingbuilding stock.Table 1.3.1 Observed Performance score

Observed PerformanceObserved Performance

Score (OPS)Nonel.ightModerateSevere/Cell apse

l O OgO50o

Observation of strong correlation between PGV and plastic deformation demands onstructural systems, together with the observed linear trend in mean plastic deformations withperiod can be combined to derive a simplified approach for performance modification. TakingGroup I mean plastic deformations as a base, one can compute the mean structural performancemodification factors (PM) for the other ground-motion groups. Figure 11 shows the results ofsuch computations for Groups III and IV by using the linear curves fitted on the exact meanplastic deformation data for periods of vibration between 0.1 and 1.0 s.

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The results are presented in Table 1.3.3. The co-efficient are rounded to integers forsimplicity.Table: 1.3.3 Initial performance scores

Initial Performance Score Vulnerability CoefficientNumber ofStories 60 < P(3V< 80 40 < P(3V


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CHAPTER 4RESULT

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CHAPTER 4RESULT

Some sample calculations are done here and the results for the buildings of the area areshown in the chart. The value of peck ground velocity (PGV) is chosen within 60< PGV


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The area of BUET Teacher's QuarterBuilding no. - 06As this building is a 4 storied building we get the values from the above table are

~o = 73 ~ss = 22aq = 0,

~AQ= 15ho =-1

~HO= 30ss =0,

So from eq 1, we getEPS = ~o + ~ss (SS) + ~AQ(aq) + ~Ho(ho)

= 73+22(0)+15(0)+30(-1)=43

Comment: The building's performance is at moderate (from table 1.3.1)

Building no. - 08As this building is a 5 storied building we get the values from the above table are

~o = 64; ~ss = 24;aq = 0;

~AQ= 23;ho =0

~HO= 33ss =0;

So from eq 1, we getEPS = ~o + ~ss(SS) + ~AQ(aq)+ ~Ho(ho)

= 64+24(0)+23(0)+33(0)=64


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Building no. - 09As this building is as storied building we get the values from the above table are

~o = 64; ~ss = 24;aq = 0;

~AQ= 23; ~HO= 33ss =0; ho =-1


= 64+24(0)+23(0)+33(-1)= 31

Comment: The building is at severe risk (from table 1.3.1)


~o = 64; ~ss = 24;aq = 0;

~AQ= 23; ~HO= 33ss =0; ho =-1


= 64+24(0)+23(0)+33(-1)= 31


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~o = 73; ~ss = 22;aq = 1;

~HO= 30ss =0; ho =-1


= 73+22(0)+15(1)+30(-1)= 58


The Chalk Bazaar areaBuilding no. - 11As this building is a 3 storied building we get the values from the above table are

~o = 80; ~ss = 23;aq = -1;

~AQ= 9; ~HO= 23ss = 0; ho= 0


= 80+23(0)+9(-1)+23(0)= 71


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~o = 73; ~ss = 22;aq = 0;

~HO=30ss =-1; ho=O


= 73+22(-1)+15(0)+30(0)= 51



~o = 80; ~ss = 23;aq = -1;

~AQ= 9; ~HO=23ss =-1; ho=O

So from eq 1, we getEPS = ~o + ~ss (SS) + ~AQ(aq) + ~Ho(ho)

= 80+23(-1 )+9( -1 )+23(0)=48


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Bakshi Bazaar areaBuilding no. - 12As this building is a 6 storied building we get the values from the above table are

~o = 64; ~ss = 24;aq = 0;

~AQ= 23; ~HO= 33ss =0; ho =-1


= 64+24(0)+23(0)+33(-1)= 31

Comment: The building is at sever risk (from table 1.3.1)

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Table 1.4.2: Calculated EPS value and comment (Buet Teachers Quarter)

Building Overall No. of Presence Presence of Apparent Building Quality EPS CommentArea of softNo. Dimension Story Overhanging Good Moderate PoorstoryBuet Teachers Quarter 1 100 x 50 5 a a 1 64 Moderate

2 100 x 50 5 a a 1 64 Moderate3 70 x 50 4 a 1 1 43 Severe4 70 x 50 4 a 1 1 43 Severe5 100 x 50 4 a a 1 73 Moderate6 70 x 50 4 a 1 1 43 Severe7 70 x 50 4 a 1 1 43 Severe8 100 x 50 5 a a 1 64 Moderate9 100 x 50 5 a a 1 64 Moderate30 70 x 50 4 a 1 1 58 Moderate45 70 x 50 4 a 1 1 58 Moderate

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Table 1.4.3: Calculated EPS value and comment (Buet Staff Quarter)

Building Overall No. of Presence Presence of Apparent Building Qualityof soft EPS CommentArea No. Dimension Story Overhanging Good Moderate PoorstoryBuet Staff Quarter 10 5 0x40 5 0 0 1 64 Moderate

11 100x40 5 0 0 1 64 Moderate1 5 5 0x40 5 0 0 1 64 Moderate14 5 0x40 5 0 0 1 64 Moderate43 70x30 5 0 0 1 64 Moderate42 70x30 5 0 0 1 64 Moderate16 5 0x40 5 0 0 1 64 Moderate17 70x30 5 0 0 1 64 Moderate1 8 40x3 0 5 0 0 1 64 Moderate5 2 70x30 5 1 1 1 3 0 Severe12 120x3 0 5 0 0 1 64 Moderate13 120x3 0 5 0 0 1 64 Moderate

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Table 1.4.4: Calculated EPS value and comment (Bakshi Bazar - Urdu Road)Buildin g Overa ll No. o f Pres ence of Presence of Apparent BuildingQuality E PS CommentArea No. Dimension Story softsto ry Overhanging Good Moderate Poor

B a k s h iB a z a r-U r d u R o a d l1/a 60x45 6 1 0 1 40 Severel1/b 60x50 6 1 0 1 63 M oderate12 50x60 2 0 1 1 48 Severe7 60x40 9 1 0 1 63 Moderate8 50x30 5 0 0 1 64 Moderate13 80x60 5 1 1 1 7 Severe14 70x45 3 1 0 1 48 Severe

15/a 50x50 3 1 0 1 57 Moderate15/b 65x50 4 0 1 1 58 Moderate16 60x45 4 1 0 1 51 M oderate20 90x70 8 1 1 1 30 Severe

20/a 85x65 6 1 1 1 7 Severe20/c 60x60 4 1 0 1 51 Moderate22 75x70 6 1 1 1 30 Severe23 100x80 8 1 0 1 63 Moderate24 55x45 3 0 0 1 80 L ight

24/a 60x50 5 1 0 1 40 Severe25 50x40 3 0 1 1 48 Severe26 75x65 5 1 1 1 7 Severe27 70x55 4 0 1 1 43 Severe28 45x65 5 1 0 1 17 Severe31 65x55 4 1 0 1 36 Severe40 60x40 4 1 0 1 36 Severe41 70x55 4 1 1 1 21 Severe43 50x45 2 0 0 1 71 Moderate44 55x55 3 0 1 1 57 Moderate45 80x65 4 1 1 1 21 Severe

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Table 1.4.5: Calculated EPS value and comment (Khaja Dayan 1st Lane)

Building Overall No. of Presence Presence of Apparent Building Qualityof soft EPS CommentArea No. Dimension Story Overhanging Good Moderate PoorstoryKhaja Dayan 1st Lane 15 80x70 3 a a 1 71 Moderate

14 50x60 2 a 1 1 48 Severe16 60x40 9 1 a 1 63 Moderate17 50x30 5 a a 1 64 Moderate18 85x50 4 1 a 1 51 Moderate19 45x30 3 a a 1 71 Moderate20 80x60 6 1 1 1 30 Severe21 70x45 1 a a 1 71 Moderate22 85x70 4 1 a 1 51 Moderate23 75x50 3 1 a 1 48 Severe25 75x70 6 1 1 1 30 Severe24 100x80 8 1 a 1 63 Moderate27 55x45 3 a a 1 80 Light29 50x45 2 a a 1 71 Moderate32 45x30 3 a a 1 71 Moderate35 80x60 6 1 1 1 30 Severe36 70x45 1 a a 1 71 Moderate37 85x70 4 1 a 1 51 Moderate38 75x50 3 1 a 1 48 Severe39 95x75 4 a 1 1 58 Moderate41 50x35 2 1 a 1 48 Severe

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Table 1.4.6: Calculated EPS value and comment (Chalk Bazar Azgor Lane)

Building Overall No. of Presence Presence of Apparent Building Qualityof soft EPS CommentArea No. Dimension Story Overhanging Good Moderate PoorstoryChalk Bazar Azgor Lane 11 55x45 3 0 0 1 71 Moderate

13 75x60 2 0 0 1 71 Moderate14 90x60 2 0 1 1 66 Moderate15/a 50x50 3 1 0 1 87 Light18 65x50 4 1 0 1 51 Moderate19 100x75 3 0 0 1 80 Light22 45x65 3 1 0 1 48 Severe23 80x55 4 0 0 1 73 Moderate24 50x45 4 1 0 1 66 Moderate25 85x70 4 1 1 1 36 Severe26 70x55 4 1 0 1 51 Moderate28 80x60 6 1 1 1 30 Severe29/b 55x50 5 1 0 1 40 Severe30 65x50 5 1 0 1 17 Severe31 90x75 7 1 1 1 30 Severe31/a 60x45 4 0 0 1 58 Moderate32 60x45 4 0 0 1 58 Moderate

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Table 1.4.7: Calculated EPS value and comment (Hosni Dalan)

Building Overall No. of Presence Presence of Apparent Building Qualityof soft EPS CommentArea No. Dimension Story Overhanging Good Moderate PoorstoryHosni Dalan 34/a 60x50 2 0 1 1 48 Severe

35 30x25 3 0 1 1 57 Moderate37 40x35 2 1 0 1 57 Moderate39 55x40 3 1 1 1 25 Severe40 35x25 3 0 0 1 80 Light17 25x20 2 1 0 1 48 Severe15/b 30x30 4 1 1 1 36 Severe14 35x25 2 0 0 1 71 Moderate13 30x25 3 0 0 1 89 Light12/a 30x25 3 1 0 1 48 Severe12/b 65x45 5 1 1 1 7 Severe11 30x35 3 0 0 1 71 Moderate14 45x50 4 0 1 1 43 Severe15 45x40 3 1 1 1 25 Severe16 75x65 5 1 1 1 7 Severe17 70x55 4 0 1 1 43 Severe10 60x40 5 1 1 1 30 Severe8 40x55 4 1 1 1 36 Severe

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Table 1.4.8: Calculated EPS value and comment (Ajimpur Colony)

Building Overall No. of Presence Presence of Apparent Building Qualityof soft EPS CommentArea No. Dimension Story Overhanging Good Moderate PoorstoryAjimpur Colony 3 2 65 x50 5 a a 1 64 Moderate

3 3 65 x50 5 a a 1 64 Moderate3 6 40x5 0 4 a a 1 73 Moderate3 9 5 0x40 4 a a 1 73 Moderate42 5 0x40 4 a a 1 73 Moderate5 4 40x5 0 4 a a 1 73 Moderate43 65 x50 5 a a 1 64 Moderate44 65 x50 5 a a 1 41 Severe5 2 65 x50 5 a a 1 64 Moderate5 5 40x5 0 4 a a 1 73 Moderate5 3 40x5 0 4 a a 1 73 Moderate48 40x5 0 4 a a 1 73 Moderate49 40x5 0 4 a a 1 88 Light5 1 40x5 0 4 a a 1 88 light5 0 40x5 0 4 a a 1 73 Moderate

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Table 1.4.9: Calculated EPS value and comment (Hori Dash Lane)

Building Overall No. of Presence Presence of Apparent Building Qualityof soft EPS CommentArea No. Dimension Story Overhanging Good Moderate PoorstoryHori Dash Lane 9 40x45 5 1 0 1 40 Severe

8 65 x45 5 1 1 1 7 Severe11 3 0x35 3 0 0 1 71 Moderate1 4 45 x5 0 4 0 1 1 43 Severe1 5 45 x40 3 1 1 1 25 Severe1 6 75 x65 5 1 1 1 7 Severe1 7 70x55 4 0 1 1 43 Severe1 9 45 x65 5 1 0 1 1 7 Severe21 65 x55 4 1 0 1 36 Severe20 60x40 4 1 0 1 36 Severe22 70x55 4 1 1 1 21 Severe23 5 0x45 2 0 0 1 71 Moderate3 3 45 x3 0 3 0 0 1 71 Moderate3 4 8 0x60 6 1 1 1 30 Severe3 6 70x45 1 0 0 1 71 Moderate3 7 8 5 x70 4 1 0 1 51 Moderate3 8 75 x50 3 1 0 1 48 Severe3 9 9 5 x75 4 0 1 1 58 Moderate

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CHAPTERSCONCLUSION

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PART 2STRUCTURAL ANALYSIS OF GROUND SUPPORTED

SLAB BY STAAD.Pro

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2.1.1 DefinitionA slab supported by ground, whose main purpose is to support the applied loads by bearing

on the ground. The slab is of uniform or variable thickness and it may include stiffeningelements such as ribs or beams. The slab may be unreinforced or reinforced with nonprestressedreinforcement, fibers, or post-tensioned tendons. The reinforcement may be provided to limitcrack widths resulting from shrinkage and temperature restraint and the applied loads. Post-tensioning tendons may be provided to minimize cracking due to shrinkage and temperaturerestraint, resist the applied loads, and accommodate movements due to expansive soil volumechanges.

The use of structural slab-on-grade construction is not common practice in Bangladeshsince the depth of frost penetration in most areas, and thus the required depth of footings, warrantthe construction of a basement. However, in situations where a basement is undesirable or whereproblem soils are encountered, a structural slab-on-grade may be preferred.

The concrete floor is often the most used, and noticed, part of the building. With thatamount of importance, one would think that we would usually get them right. Unfortunately, it isall too rare that the concrete floor meets the criteria of Owner, design professional and contactorthroughout the life of the building.

Fig: 2.1.1 Slab-on-ground

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As structural slab-on-grade construction is not common practice, builders unfamiliar withits use may encounter problems with construction.2.1.2 Installing Slabs on Grade

An area of the floor system that is crucially important is the sub-grade on sub-base. Themost important item is proper compaction; many floors settle and have structural cracks. Ofcourse, organic material cannot be properly compacted and must never be in the sub-grade. It is asimple fact that the floor system rests on the grade and if the sub-grade settles, the floor settles.

Forming of concrete floors is reasonably straightforward. One must remember, though, thatloose or warped edge forms cause uneven floors. Therefore, the care taken with the edge formsetting will be proportional to final flatness of the floor.

Placing concrete in hot weather, particularly when the walls and roof are not yet completed,creates some additional quality concerns. Plastic cracking is one of the worse problems thatoccur. Plastic shrinkage cracks form before the concrete hardens and are caused by hot, dry,and/or windy conditions. The cracks resemble the shrinkage cracks seen in clay soils during verydry weather.Curing can also create many problems for concrete floors. Since water evaporates so quicklyfrom the large exposed surface, without proper curing methods a floor is likely to rack, craze anddust. The three most common means of curing are:

1. Wet cure by covering, after finishing, with continuously watered burlap.2. Wet cure by watering finished slab and covering with plastic or paper.3. Seal cure with liquid membrane curling compound.

2.1.3 Failure of ground supported slabsFailure of ground-supported slabs is all too common. Unequal settlement, overloading and

restrained shrinkage and thermal displacement all tend to produce cracking. The passage ofwheel loads over crack or improperly made joints often leads to failure by progressivedisintegration of the concrete. Slab failure, when they occur is not spectacular and do not resultsin collapse in the usual scene, but the use fullness of the slab may be gladly simpered, and repairsare often costly.

Design methods for slab on ground vary. There is a common theoretical basis that assumeshighly idealizes conditions, but results are modified in recognition of test data and practicalexperience. Generally, the design is based in natural service loads and concrete stress that arecompacted against specified limit. Steel reinforcement are used is placed mainly for crack

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control, although more modem method of analysis and design account for its contribution in astructural scene.

2.1.4 Shrinkage and temperature effectsA concrete pavement slab, unloaded except for its self-weight. Concrete Shrinkage

or a decrease in temperature, tends to contract the slab, but this contraction is resisted byfrictional drug between the slab and the sub grade. This causes tensile forces in slab. If the totallength of slab between construction joints is 1,than equilibrium of the horizontal forces for onehalf the length for unit strip of slab indicates that the tension force at a cross section at the midlength is

Where,Wo = self weight of pavement slab, psi!l = coefficient of friction between slab and subgrade1= length between contraction or contraction jointsT = tensile force

The coefficient of friction varies widely, depending mainly on the roughness of the subgrade, and tests show a range between about 1 and 2.5. The coefficient may be less than 1.0 ifplastic film is used between the slab sub grades. For design of highway pavement the AASHTO.Interim Guide assumes a value of 1.5. If the slab has not tensile stress in psi is

f t = T / 12hWhere h is the thickness in inches.

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f i ' 1 i 1 i i i m U I i l f I ' 1 6 1 ~2 ~ N lI i" a OfIt1I~e~-]% 3ii~emrainment

4!"~< lkml l l~ "o : !~ng~~ !~" IM~ld~rn4!"o:!~g~~!

1.~2){IS2 MW

i~i~ 1 1 1 , . 1 1 1 1 .I V l i ; g jd r o a mMiI1IiInUrll,b" deant : r


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Inadequate structural strengthof concrete

Frost heave

Improper placementreinforcing and mesh

Ensure the slab is properly designed to Part 4 of theNational Building Code.Use concrete with sufficient compressive strength, at least25 MPa, but preferably 30 MPa.

Never pour concrete on a frozen subgrade. Maintain above-freezing temperatures in the house during

construction. Use adequate insulation to reduce the depth of frost

penetration.Use proper installation techniques, including: Locate mesh no more than 50 mm below the surface of the

slab.Lap meshes at least one square.Use chairs to support the mesh at the correct height duringconcrete pouring.Ensure the minimum concrete cover over reinforcing steelis at least 76 mm.

Lap steel at least 24 bar diameters, but at least 300 mm

of

Table: 2.1.2 Damp or wet floor slab, excessive humidity

Problem: Damp or wet floor slab, excessive humidityCause Solution

Moisture migration through the Provide a capillary break (for example, a granular layer)slab under the floor slab. Provide perimeter drainage and/or a sump pump.Air leakage through the slab Eliminate cracks and holes in the slab, seal around pipes,drains and ducts, use traps in drains.

Damp proof the slab, either on top using at least twoWater vapor diffusion through mopped-on coats of bitumen where a separate finishedthe slab floor is provided, or under the slab using at least 0.15 mm

polyethylene or Type S roll roofing. Provide good site drainage by sloping the subgrade and allPoor site drainage surface grades away from the house and draining

downspouts away from the house.

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CHAPTER 2LITERA TURE REVIEW

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CHAPTER 2LITERATURE REVIEW

2.2.1 IntroductionReview of classical design theories-Design methods for slabs-on-grade are based on

theories originally developed for airport and highway pavements. Westergaard developed one ofthe first rigorous theories of structural behavior of rigid pavement (Westergaard 1923, 1925,1926).

This theory considers a homogeneous, isotropic, and elastic slab resting on an idealsubgrade that exerts, at all points, a vertical reactive pressure proportional to slab deflection;known as a Winkler subgrade . The subgrade acts as a linear spring with a proportionalityconstant k with units of pressure (lblin). 2 [kl'aj) per unit deformation (in. [mj). The units arecommonly abbreviated as lblin. 3 (kN/m3). This constant is defined as the modulus of subgradereaction.

In the 1930s, the structural behaviors of concrete pavement slabs were investigated at theArlington Virginia Experimental Farm and at the Iowa State Engineering Experiment Station.Good agreement occurred between experiential stresses and those computed by theWestergaard's theory, as long as the slab remained continuously supported by the subgrade.Corrections were required only for the Westergaard comer formula to account for the effects ofslab curling and loss of contact with the subgrade. Although choosing the modulus of subgradereaction was essential for good agreement with respect to stresses, here remained ambiguity inthe methods used to determine the correction coefficient.

All existing design theories are grouped according to models that simulate slab and thesubgrade behavior. Three models used for slab analysis are:

Elastic-isotropic solid; Thin elastic slab; and Thin elastic-plastic slab.

Two models used for subgrade are:1. Elastic-isotropic solid; and2. Winkler (1867).

The Winkler subgrade models the soil as linear springs so that the reaction is proportionalto the slab deflection. Existing design theories are based on various combinations of thesemodels. The methods in this guide are generally graphical, plotted from computer-generatedsolutions of selected models. Design theories need not be limited to these combinations. The

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elastic-isotropic model provides close prediction for the response of real soils, but the Winklermodel is widely used for design and a number of investigators have reported good agreementbetween observed responses to the Winkler-based predictions.2.2.2 Finite-element method

The classical differential equation of a thin elastic plate resting on an elastic subgrade isoften used to represent the slab-on-ground. Solving the governing equations by conventionalmethods is feasible for simplified models where slab and subgrade are assumed to be continuousand homogeneous. In reality, a slab-on-ground usually contains discontinuities, such as jointsand cracks, and the subgrade support may not be uniform. Thus, the use of this approach islimited.

The finite-element method can be used to analyze slabs-on-ground, particularly those withdiscontinuities. Various models have been proposed to represent the slab (Spears and Panarese1983; Pichumani 1973). Typically, these models use combinations of elements, such as elasticblocks, rigid blocks, and torsion bars, to represent the slab. The subgrade is typically modeled bylinear springs (Winkler subgrade) placed under the nodal joints. Whereas the finite-elementmethod offers good potential for complex problems, graphical solutions and simplified designequations have been traditionally used for design. The evolution of modem computer softwarehas made modeling with finite elements more feasible in the design office setting.

2.2.3 Construction document informationListed below is the minimum information that should be addressed in the construction

documents prepared by the designer. Refer to ACI 302.1R for information related to theinstallation and construction for some of these items. Slab-on-ground design criteria; Base and subbase materials, preparation requirements, and vapor

retarder/barrier, when required; Concrete thickness; Concrete compressive strength, or flexural strength, or both; Concrete mixture proportion requirements, ultimate dry shrinkage strain, or

both; Joint locations and details; Reinforcement (type, size, and location), when required; Surface treatment, when required; Surface finish;

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Tolerances (base, subbase, slab thickness, and floor flatness and levelness); Concrete curing; Joint filling material and installation; Special embedment's; Testing requirements; and Preconstruction meeting, quality assurance, and quality control.

2.2.4 Slab-on-ground design criteriaIt is helpful that when the slab-on-ground design criteria are well established, that it be

shown on the drawings. This information is especially useful when future modifications aremade to the slab or its use. Design issues, such as the slab contributing to wind or seismicresistance or building foundation uplift forces, would not be readily apparent unless noted on thedrawings. Because it is not readily apparent when a slab is used as a horizontal diaphragm, itshould be noted on the drawings. Removing or cutting a slab that is designed to resist uplift orhorizontal forces could seriously impair the building's stability.

The design criteria should include some of the following: Geotechnical soil properties used for the different loading types; Uniform storage loading; Lift-truck and vehicle loadings; Rack loadings; Line loads; Equipment loads; When the slab is used to resist wind or seismic foundation uplift forces; & When the slab is used as a horizontal diaphragm and to resist horizontal

forces or both due to tilt-walls, masonry walls, tops of retaining walls, andmetal building system columns.

Further researchThere are many areas that need additional research. Some of these areas are:

Developing concrete mixture proportions that have low shrinkage characteristicsand are workable, finish able, and provide a serviceable surface; Flexural stress in slabs with curl and applied loads and how curling stresses

change over time due to creep; Base restraint due to shrinkage and other volume changes and how this restraint

changes over time; Crack widths for different amounts of reinforcement for slabs-on-ground; Provide guidance on acceptable joint and crack widths for different slab usages;

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Provide dowel recommendations based on loadings (lift truck, rack post, anduniform storage) rather than slab thickness;

Provide plate dowel spacing recommendations for plate dowel geometries; Provide design guidance for slabs with macro synthetic fibers; Provide design aids for slabs with rack uplift loads due to seismic and other uplift

loadings; Provide design aids for slabs with non-uniform rack post loads; Develop a standardized method for testing and specifying slab surface abrasion

resistance; Soil properties and how they may change over time under load repetitions, wide

area long-term loadings, or both; and Recommended joint spacing for fiber-reinforced concrete.

2.2.5 DefinitionsCurling or warping - Out-of-plane deformation of the comers, edges, and surface of a

pavement, slab, or wall panel from its original shape.Slab-on-ground - slab, supported by ground, which is main purpose, is to support the

applied loads by bearing on the ground.Some of the more important expectations that should be discussed for the prospective slab

type are: Cracking potential; Crack widths for slabs designed with reinforcement to limit crack widths; Use of doweled joints versus aggregate interlock; Possible future repairs including joint deterioration; Joint maintenance requirements and the owner's responsibility for this

maintenance; Floor flatness and levelness requirements to meet the owner's needs; Changes to the flatness and levelness over time, especially in low -humidity

environments; Advantages and disadvantages of slab placement with the watertight roofing

system in place versus placing the slab in the open; Level of moisture vapor resistance required; and Advantages and disadvantages of using the building floor slab for tilt-wall

construction form and temporary bracing.

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Slab typesThere are four basic design choices for slab-on-grade construction:

a. Unreinforced concrete slab.b. Slabs reinforced to limit crack widths due to shrinkage and temperaturerestraint and applied loads. These slabs consist of:

1. Nonprestressed steel bar, wire reinforcement, or fiber reinforcement,all with closely spaced joints; and

ii. Continuously reinforced, free-of-saw cut contraction joints.c. Slabs reinforced to prevent cracking due to shrinkage and temperature

restraint and applied loads. These slabs consist of:i.Shrinkage-compensating concrete; andii.Post-tensioned.d. Structural slabs designed in accordance with ACI 318:

i.Plain concrete; andii.Reinforced concrete.

apor retar en arrier(Note: See Fig ..4..7 forinformation on locatingthe vapor retarder/barrier.)

Load

SlabBase

Subbase

Subglrade

Fig: 2.2.1 - Slab support system terminology.

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2.3.1 IntroductionConcrete slabs are often poured directly on the ground; they receive uniform support from

the soil. Roadway and sidewalk slabs, basement floors, and warehouse floors are commonexamples of this type of construction. Ordinary it is desirable to provide a base course of wall-complicated crushed stone or gravel. The prepared subgrade, approximately 6 to 12 in, thick,serves (1) to provide more uniform support than if the slab were carried directly on the on thenatural soil, and (2) to improve then drainage of water from beneath the slab. The latter isparticularly important in outdoor locations subjects to freezing temperatures.

Failures of concrete slabs on ground are not infrequent. Unequal settlement or overloadingmay cause cracking, as well as restrained shrinkage as volume changes occur. Passing of wheelloads over cracks or improperly made joints may lead to progressive failure by disintegration ofthe concrete. Failures are not spectacular and do not involve collapse in the usual sense. Theymay even pass unnoticed for a considerable period of time. Nevertheless, the function of thestructure is often impaired and repairs are both embarrassing and costly.

It is the slab is loaded uniformly over its entire areas and is supported by a uniform, subgrade; stresses will be due solely to restrained volumetric changes. However, foundationmaterials are not uniform in their properties. In addition, most slabs are subjected to no uniformloading.

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2.3.2 MethodologyMethods of analysis for slab on grade are similar to those developed for beams on elastic

foundations. Usually the slab is assumed to be homogenous, isotropic and elastic; the reaction ofthe sub grade is assumed to be only vertical and proportional to the defection. The stiffness of thesoil is expressed is terms of the modulus of subgrade reaction is usually in units of ton per in, orsimply, lb per in. The numerical value of k varies widely for different soil types and degrees ofconsolidation and is generally based on experimental observation.

The usual method of constructing a structural slab-on-grade is to use a thickened slab; atthe edges of the slab, where most of the load will be carried, the slab is thickened, the thickenedportion being cast integrally with the rest of the slab.

For the analyze, concentric loads may be placed according to following three cases. Thoseare as follows-Case 1:Wheel load close to the comer of a large slab:

With a load applied at the comer of a slab, the critical streets in the concerts are tension atthe top surface of the slab. An approximate solution due to A.T. Gold back, assumes point loadacting at the comer of the slab. At small distances (from the comer, the upgrade reaction of thesoil has little effect and the slab is considered to act at a cantilever. At a distance z from thecomer, the bending moment is pz; it is assumed to be uniformly distributed across the width ofthe section of slab at right angles to the bisector of the comer angle. For a 900 comer, the widthof the section is 2r and bending moment per unit width of slab is

Pz P- -2z 2If h is the thickness of the slab, the tensile stress at the top surface is

Equation (4.5) will give reasonably close results only in the immediate vicinity of the slabcomer, and if the load is applied over a small contact are:

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In an analysis which considers the reaction of the sub grade and which consider the load tobe applied over a contact area of radius 0 (see Fig: ...) West guard derives the expression forcritical session at the top of the slab, occurring at a distance ~ from the comer of the slab:

In which L is the radius of relative's stiffness, equal to

Where E elastic modulus of concrete, psiP Polson's ratiok modulus of subgrade reaction, Ib/in2

The value of L reflects the relative stiffness of the slab and the sub -grade. It will be largefor a stiff slab and slot base and small for a flexible slab on a still base.

Case 2: wheel load considerable distance fronts the edges of a slab:With the load is applied some distance from the edges of the slab, the article stress into the

concrete will be tension at the bottom surface. That tension is greatest directly under the centerof the loaded area and is given by the expression.

fy =0.316 ~ [log h2 -4log(~1.6a2 +h2 -0.675h) -log k+6.48) (4.9)h

Case 3: wheel load at an edge of a slab, but removed a considerable distance from a comer:When the load is applied at a point along an edge of the slab, the critical tensile streets is at

the bottom of the concrete, directly under the load, and is equal to

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fx=0.S72 ~ (logh2_4 log~1.6a27h2-0.675h) -logk+S.77]hIn the event that the tensile stress in the slab, as given by Eqs. (4.7), (4.9) and (4.10)

exceeds the allowable tensile streets on the concrete, it is forcemeat. Such reinforcement isusually designed to provide for the entire slab. Its centroid should be no closer to the neutral axisthan that of the tension concrete, which is replaces.

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CHAPTER 4RESUL T AND DISCUSSION

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CHAPTER 4RESULT AND DISCUSSION

Results are shown in the chart for the three cases of loading. Self Weight (SW) is added inall calculations. The slab shows different behavior under different cases. The results for nodedisplacement, principle stress and bending moment are shown below and analyzed by the graphs.

For 15'-15' SlabTable: 2.4.1

Node displacement (15-15) for Corner + Self weight

Distance LIC Vertical VerticalNode Yin Node Yin0 Comer + SW 1 -0.029 7 -0.0231 Comer + SW 5 -0.023 6 -0.0182 Comer + SW 8 -0.017 9 -0.0143 Comer + SW 10 -0.012 11 -0.014 Comer + SW 12 -0.009 13 -0.0075 Comer + SW 14 -0.006 15 -0.0056 Comer + SW 16 -0.004 17 -0.0047 Comer + SW 18 -0.003 19 -0.0038 Comer + SW 20 -0.0025 21 -0.0029 Comer + SW 22 -0.002 23 -0.00210 Comer + SW 24 -0.002 25 -0.00211 Comer + SW 26 -0.002 27 -0.00212 Comer + SW 28 -0.002 29 -0.00213 Comer + SW 30 -0.002 31 -0.00214 Comer + SW 32 -0.002 33 -0.00215 Comer + SW 2 -0.002 34 -0.002

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Load 5 :Displacement

Figure: 2.4.1: Displacement of 15-15 ft slab for corner loading

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-0.01I. . . .I:C IJEC IJu'"'iiiis-0.02

-0.03

o 10 20 25 305 15


-0.025

o

25

Distance (ft.)

Deflection Curve along edge (outside) of slab (15-15) due toCorner load + Self WeightFigure: 2.4.2

o 10 15 2050.005

Distance (ft.)

Deflection Curve along very next to edge of slab(15-15) due toCorner load + Self WeightFigure: 2.4.3

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Table: 2.4.2

Node displacement OS-IS) for Edge + Self Weight

Distance Lie Vertical VerticalNode Yin Node Yin0 Edge + SW 1 -0.003 7 -0.0021 Edge + SW 5 -0.003 6 -0.0032 Edge + SW 8 -0.004 9 -0.0043 Edge + SW 10 -0.0055 11 -0.0054 Edge + SW 12 -0.007 13 -0.0065 Edge + SW 14 -0.009 15 -0.0076 Edge + SW 16 -0.011 17 -0.0097 Edge + SW 18 -0.013 19 -0.018 Edge + SW 20 -0.013 21 -0.019 Edge + SW 22 -0.011 23 -0.00910 Edge + SW 24 -0.009 25 -0.00711 Edge + SW 26 -0.007 27 -0.00612 Edge + SW 28 -0.0055 29 -0.00513 Edge + SW 30 -0.004 31 -0.00414 Edge + SW 32 -0.003 33 -0.00315 Edge + SW 2 -0.003 34 -0.002

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Load 6 :Displacement

Figure: 2.4.4: Displacement of 15-15 ft slab for edge loading

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-0.03

o 10 20 25 305 15


-0.025

o

25

Distance (ft)Deflection Curve along edge (outside) of slab (15-15) due to

Edge load + Self WeightFigure: 2.4.5

o 10 15 2050.005

Distance (ft)Deflection Curve along very next to edge of slab(15-15) due to

Edge load + Self WeightFigure: 2.4.6

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Table: 2.4.3Node displacement OS-IS) Center + Self Weight

Distance LIC Vertical VerticalNode Yin Node Yin0 Center + SW 116 -0.002 132 -0.0021 Center + SW 115 -0.002 131 -0.0022 Center + SW 117 -0.003 133 -0.0033 Center + SW 118 -0.003 134 -0.0034 Center + SW 119 -0.004 135 -0.0045 Center + SW 120 -0.004 136 -0.0046 Center + SW 121 -0.005 137 -0.0057 Center + SW 122 -0.006 138 -0.0068 Center + SW 123 -0.006 139 -0.0069 Center + SW 124 -0.005 140 -0.00510 Center + SW 125 -0.004 141 -0.00411 Center + SW 126 -0.004 142 -0.00412 Center + SW 127 -0.003 143 -0.00313 Center + SW 128 -0.003 144 -0.00314 Center + SW 129 -0.002 145 -0.00215 Center + SW 130 -0.002 146 -0.002

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