Strategies to Teach Wind Engineering Fundamentals to UndergraduateStudents

Gustavo E. Pacheco1, Héctor J. Cruzado2

1 Professor, Civil and Environmental Engineering Department, Polytechnic University of PuertoRico, San Juan, Puerto Rico, USA, gpacheco@pupr.edu

2 Associate Professor and Graduate Program Director, Civil and Environmental EngineeringDepartment, Polytechnic University of Puerto Rico, San Juan, Puerto Rico, USA,

hcruzado@pupr.edu

ABSTRACT

The topic of Building Loads is essential in a Civil Engineering Undergraduate Curriculum. Thesubject of gravity loads is easily introduced, but natural-hazard related loads (such as wind andearthquake effects on buildings) are more difficult to address, due to the lack of formation ofundergraduate students in advanced topics such as structural dynamics and advanced fluiddynamics. In order to overcome this situation, and to foster students’ comprehension of theseadvanced topics, the traditional lecture could be complemented with an heuristic approach,using resources and developing activities that stimulate the development of an behavioralunderstanding of the phenomena. This article summarizes this approach at PolytechnicUniversity of Puerto Rico, and presents examples of class projects in which the studentsenvisioned and developed specific models and devices in order to demonstrate fundamentalconcepts of wind loads on building

INTRODUCTION

The Civil Engineering Curriculum at Polytechnic University of Puerto Rico (PUPR) develops theStructural Engineering Area throughout three Engineering Science courses (Statics, Mechanicsof Materials I and II), one laboratory course (Mechanics of Materials Laboratory) and five corecourses (Theory of Structures I and II, Steel Structures Design, Concrete Structures Design, andFoundations Design).

The topic of Building Loads is essential in this curriculum, to support the design courses, and toallow the development of realistic problems in the analysis courses. This topic is developed aspart of the first Structural Analysis course (Theory of Structures I), based on ASCE-7 [1], UBC-97 [2] and IBC-06 [3] standards. Almost one third of the course is devoted to building loads(determination and distribution, with emphasis in Load Paths), one third to approximate methodsof analysis of buildings under gravity and lateral loads, and one third to the analysis of staticallyindeterminate structures by the Force Method.

The subject of gravity loads is easily introduced, but natural-hazard related loads (such as windand earthquake effects on buildings) are more difficult to address, due to the lack of formation ofundergraduate students in advanced topics such as structural dynamics and advanced fluiddynamics. In order to overcome this situation, and to foster students’ comprehension of theseadvanced topics, the traditional lecture could be complemented with an heuristic approach, usingresources and developing activities that stimulate the development of an behavioralunderstanding of the phenomena. Two activities are considered key to this end:

The intensive use of adequate visual aids and schematics that help students understandthe discussed behavior, such as those use by Schodek [4], Ambrose [5], Taly [6], andMehta [7]. An example of such visual aids is presented in Figure 1.

Figure 1: The effect of external pressure on windward wall, side wall and roof [7]

The development of students’ team projects that stimulate reasoning and visualization ofthe structural behavior, critical thinking, independent research, and synthesis of theconcepts discussed during the class period, reaching a higher taxonomic level of learning.The students have to propose, justify, explain, develop, and demonstrate a device ormodel that helps visualize and verify the concepts, procedures, and code basedcomputations discussed in class.

This paper will present different projects in which the students envisioned and developedspecific models and devices in order to demonstrate fundamental concepts of wind loads onbuilding.

METHODOLOGY

The students are required to perform a team project (to be presented to the whole class) byselecting one of the following five alternatives:

Envision and develop a model that demonstrates a particular response discussed in class. Perform the load analysis (Dead, Live, Wind and Earthquake) of a real building.

Develop a computer program (software) that implements one of the topics discussed inthe class.

Develop a computer model of a real building, perform its analysis and compare resultswith approximate method of analysis (i.e., tributary areas).

Develop a set of challenging problems assigned by the professor.

The students that opt for the first alternative have to develop their project in a four-stage process,as described bellow:

The students select a topic among the subjects discussed in class that is of particularinterest for the team members. The selected topic is presented to the professor forapproval, and the project scope is defined, specifying the behavior that wants to beobserved.

The students perform a literature review and have brainstorming sessions to conceive amodel that could exemplify the expected response.

The students build the model and assess its suitability, proposing and implementingimprovements, if applicable.

The students develop a detailed written report of the project, and conduct an oralpresentation in front of their peers with the objective that all the students of the course areable to visualize and understand the targeted response.

OUTCOMES

A series of students projects are presented and briefly described in this section as examples of theoutcomes achieved by the students in their quest to qualitatively demonstrate and help visualizewind related structural response:

In the first example, shown in Figure 2, students proposed a model developed todemonstrate the effect of the external wind pressure or suction on a prismatic shapedbuilding with square floor plan. Students used wood studs for the building frame (in orderto have a stiff structure) and transparencies for the walls and the roof, in order to haveflexible elements that clearly show the inward deflection produced by the positivepressure, and the outward deflection produced by the negative pressure. They used a fanas a wind generator. The model helps to understand the general load pattern due toexternal pressure in a regular building and the sign of the pressure coefficient given inASCE-7 [1] for the windward, leeward and side walls, and for the roof.

The second example consists of a model developed to visualize the effect of the internalpressure on a regular building, helping in the understanding of the inclusion of sucheffect in the code specifications. The model consisted of a rigid frame with flexible wallsand roof (both made off nylon sheets), with a front door that can be opened in order tosimulate a partially enclosed building. They use a fan as a wind generator. Figure 3 (a)presents the effect of wind over an enclosed regular building, while Figure 3 (b) presentsthe effect when the front door is opened, giving place to the building up of the internalpressure and a substantial increase in the total resulting pressure in the side walls and theroof, as evidenced by the larger deflection of the membrane.

Figure 2: Roof without (a) and with (b) wind action, windward wall and side wall without (c) and with (d)wind action.

Figure 3: Internal pressure effect in (a) closed building and (b) partially enclosed building

(a) (b)

(a) (b)

(c) (d)

The third example, presented in Figures 4 and 5, presents a device envisioned todemonstrate the effect of the building shape in the wind flow pattern by comparing acubic shaped building to a dome shaped (geodesic) structure. They used wood and acrylicfor the device, a fan and a vacuum cleaner to produce the air movement, and dioxidecarbonate in solid state to trace the air flow stream pattern with the help of ultravioletlight. Although the students committed the error of making the building models too largefor the size of the device so the expected behavior was not clearly demonstrated, theproject was very creative and interesting.

Figure 4: Device to demonstrate the effect of building shape in wind streams.

Figure 5: Close up to the device.

In the fourth example the students presented a model to demonstrate the effect of therelative beam to column stiffness in a moment resisting frame building response whensubjected to lateral loads (such as wind loads). Figure 6 (a) shows the deflected shapewhen beam and column have similar stiffness, showing a beam inflection point near midspan, and a column inflection point upper to column mid height. Figure 6 (b) displays thestrong column-weak beam case, with the columns acting almost as cantilever elements,and the beams as very flexible elements with the inflection point at mid span. Figure 6 (c)illustrates the weak columns-strong beam case, with the columns experiencing theinflection point at mid height and the beam moving as a rigid body. The visualization ofthis type of behavior helps understand the hypothesis used in simplified methods ofanalysis of frames under lateral loads, such as the Portal Method.

Figure 6: Frame under lateral load: (a) beam and columns with similar stiffness, (b) stiff columns flexiblebeam, and (c) flexible columns stiff beam.

The last example presents a model developed by the students to demonstrate the vibrationmodal shapes and natural periods of a flexible structure (more prone to be dynamicallyaffected by wind actions). The structure is a two degree of freedom system, with columnsmade of plastic pipes and concentrated masses made of heavy wooden blocks, shown inFigure 7. The experimental values obtained for the natural period were critically analyzedin terms of their magnitude, and compared to the ones obtained by computer basednumerical models. This type of model supports the visualization of dynamic modalresponse, and allows proving the period of the load that produces amplification of thesystem response (resonance) indicating that a dynamic analysis is required in suchcircumstances.

(a) (b) (c)

Figure 7: Flexible structure dynamic modal response

SUMMARY, CONCLUSIONS AND FUTURE WORK

A strategy of complementing the traditional lecture with students’ team projects that stimulate thedevelopment of a behavioral understanding of the effect of wind over building structures was presented,and some of the outcomes were described. These projects, although having lead to the developmentof simple and limited models and devices, have shown to be a powerful tool of visualization of

the fundamentals of the phenomena, and have serve as motivation for the students to criticallyanalyze and synthesize this basic concepts and procedures, and to get involved in the class.

This type of projects does not require special facilities and equipment, but they could becomplemented with more sophisticated and resource demanding analysis such as the use of awind tunnel and computer simulations. A proper outcomes assessment process should bedeveloped in order to evaluate the impact that the presence or lack of this type of projects wouldhave in the students comprehension of the topic.

A new laboratory course, at a senior level, will be developed in order to allow more advancedstructural engineering modeling and testing, and complement the type of projects presented inthis article with quantitative measures.

ACKNOWLEDGEMENT

The authors would like to thank PUPR Civil and Environmental Engineering Department(CEED) continuous support, and CEED students for their fine job and dedication.

REFERENCES

[1] American Society of Civil Engineers (ASCE), Minimum Design Loads for Buildings and OtherStructures, (ASCE/SEI 7-05), Reston, VA, 2005.

[2] International Conference of Building Officials (ICBO), Uniform Building Code, Volume 2, Whittier,CA, 1997.

[3] International Code Council (ICC), International Building Code, Lenexa, KS, 2006.

[4] Schodek, D. L., Structures, Pearson Prentice Hall, Upper Saddle River, NJ, 2004.

[5] Taly, N., Loads and Load Paths in Buildings: Principles of Structural Design, ICC, Lenexa, KS, 2003.

[6] Ambrose, J. and Vergun D., Simplified Building Design for Wind and Earthquake Forces, John Wileyand Sons, New York, NY, 1997.

[7] Mehta, K. C., Wind Protective Design Course, Multi-protection (Multi-hazard) Building DesignSummer Institute, Federal Emergency Management Agency, 1995.