| Author | Lin, Min-shay |
| Call Number | AIT Thesis no. ST-91-16 |
| Subject(s) | Tall buildings--Earthquake effects
|
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of master of engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | When buildings with asymmetric plan (non-coincident center of mass and center of stiffness)
are subjected to earthquake motions they undergo coupled torsional lateral movements. The seismic
response of such a building will be influenced by the foundation soil properties, particularly,
if the soil is soft. This thesis is concerned with the seismic response of three dimensional asymmetric
multi-storey buildings, including the foundation interaction effects.
The structural model considered in this study is a three dimensional linear elastic N-storey
asymmetric shear building resting on the surface of an elastic half-space. Each floor has three
displacement degrees of freedom, namely two orthogonal translations and one twist. In addition,
the foundation may be subjected to two lateral, two rocking and one torsional movements. Thus,
the system has a total of 3N+5 degrees of freedom. The ground excitation has been assumed
to be along two orthogonal directions, simultaneously. Three equations of motions for each
floor have been developed about the center of mass, which gives a total of 3N equations. Five
more equations have been developed considering the two translations, two rockings and one twist
of whole system. The last five equations contain structure-foundation interaction forces written
in a frequency independent form.
The 3N+5 equations are, in general, coupled equations, and cannot be solved directly.
However, assuming that the superstructure admits classical normal modes, the response of the
superstructure can be written in terms of normal mode shapes and unknown normal coordinates.
The uncoupled solution for unknown normal coordinates may be ·obtained by Duhamel' s integrals,
however, they are in terms of base movements. The substitution of these solutions into the remaining
equations gives five integrodifferential equations, in terms two base displacements , two base
rocking angles and one base twist. These five equations can be solved numerically. Once the base
displacements are known the unknown normal coordinate can be obtained by back substitution.
Then the each floor movements may be obtained by appropriate transformations. Finally stress
resultants such as floor shear forces can be obtained from structural deformation. The computational
efficiency can be improved further by identifying and applying only few of the significant
classical normal modes.
-lVThe convergence study of time step of number of mode shape have shown that time step of
0.02 sec and first 10 normal mode shapes of the superstructure are sufficient to obtain the accurate
results.
Results are presented for a typical 10-storey asymmetric building having a rectangular plan.
The effects of soil-structure interaction do affect the response of response of structure. The soils
with the shear wave velocity of 1667 ft/sec can be treated in the analysis/design as rigid foundation.
Based on the effects of eccentricity on response of floor twist and floor torque we should consider
the effects of eccentricities when we design structure for earthquake. |
| Year | 1991 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Structural Engineering (STE) /Former Name = Structural Engineering and Construction (ST) |
| Chairperson(s) | Karasudhi, Pisidhi ;Sivakumaran, K.S.
|
| Examination Committee(s) | Yamaguchi, Hiroki
|
| Scholarship Donor(s) | The Government of The Republic of China |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1991 |