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CHAPTER 4

EQUIVALENT LATERAL FOCE METHOD

4.1. INTRODUCTION

Equivalent lateral force procedure is a simplified analysis procedure that as stated in section 17.4.1 of ASCE -16 can be applied to certain structures having regular horizontal and vertical geometry and limited number of stories. The structure is

analyzed using equivalent lateral force procedure, ELF for both upper and lower bound properties of the isolation system. The building is analyzed for design

earthquake loading with upper bound properties and for MCER earthquake with lower bound properties, this is because the resultant displacements is creating a boundary as the smallest and largest displacements and the displacements from DE

loading with lower bound properties and MCER loading with upper bound properties will fall between the above mentioned values. The potential for uplift is

checked using SAP2000. The calculations follow ASCE 7-16, section 17.5. Since the resultant vertical force in the upper stories is more than what will be produced using

ASCE 7-10 procedure of vertical distribution. It should be noted that the building is required to remain elastic; therefore it is analyzed using RI equal to 1

4.2. ANALYIS RESULTS

The results of the ELF analysis for both upper and lower bound properties are summarized here. Detailed calculations and information is provided in the

subsequent sections. It should be noted that in subsequent chapters, X direction refers to the longitudinal and Y refers to the transvers direction of the building.

Table 4 1 Key parameters calculated using ELF for design earthquake, DE

KD TD DD DTD (x-dir)

DTD (y-dir)

Vb Vst

kip/in sec in in in kip kip

341.16 3.15 9.25 10.17 10.17 3155.69 3155.69

Note: DTD for x and y direction is same, since same factor of 1.1 was used per exception of section 17.5.3.5 of ASCE 7-10

Table 4 2 Key parameters calculated using ELF for design earthquake, MCER

KM TM DM DTM (x-dir)

DTM (y-dir)

Vb Vst

kip/in sec in in in kip kip

148.55 4.77 29.4 32.3 32.3 4368.3 3804.92

Note: DTM for x and y direction is same, since same factor of 1.1 was used per

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exception of section 17.5.3.5 of ASCE 7-10

Table below shows the maximum and minimum axial load on bearings due to various load combinations.

Table 4 3 Maximum and minimum axial load on bearing from various load combinations

Combination Description A1 A6 D6

COMB1 1 DEAD + 0.5 LL 149.90 303.14 600.38

COMB2 (UB) 1.2 DEAD + 1 LL + 0.3 VERT_EQ + EQH 306.13 557.34 943.07

COMB3 (UB) 0.9 DEAD - 0.3 VERT_EQ + 1 EQH -3.37 155.40 307.60

COMB2 (LB) 1.2 DEAD + 1 LL + 0.3 VERT_EQ + EQH 308.98 560.41 943.07

COMB3 (LB) 0.9 DEAD - 0.3 VERT_EQ + 1 EQH -6.68 155.35 307.59

NOTE: UB stands for Upper Bound, LB for Lower Bound and VERT_EQ for vertical

Effects of earthquake and EQH for vertical load due to horizontal earthquake effects

Table 4 4 Building Uplift from ELF analysis

Load Combination Joint Tension in joint (kip) Vertical Joint Displacement (in)

COMB6 (UB) F12 -15.334 0.02

COMB6 (LB) F12 -18.983 0.03

COMB7 (UB) A1 -3.372 0.004

COMB7 (LB) A1 -6.681 0.008

Detailed analysis calculations and SAP2000 modeling details are provided below.