Abstract:
This thesis presents a study on seismic design provisions which are appropriate to Thailand.
This investigation involves the base shear formulas in accordance with the Thailand Ministerial Regulation
No 49 (B.E.2540), the Uniform Building Codes UBC-1994 and 1997, the Australian Standards AS 1170.4-1993,
the American Society of Civil Engineers ASCE7-02. Based on these codes, structural response spectra have been
developed for the Seismic Zones No 1 (low risk) and No 2 (moderate risk). Comparative study of response spectra
has been attained using three distinct soil classifications: shales, stiff soils, and soft soils. The results are used as
a guidance for the amendment of the Ministerial Regulation No 49. The aim of the revision is to include the areas
of Bangkok Metropolis and its vicinities as well as other hazardous areas of Thailand into the provisions for optimum
seismic resistant design.
Based on this study, the current Thailand Ministerial Regulation No 49 is not suitable for the seismic design of buildings
rested on well-known Bangkok soft clay. The worst-case scenario could happen for buildings, unless the base shear
formula have been carefully rectified.
In particular, it is found that the use of soil coefficient (S) of 2.5 and CS value less than or equal to 0.25 leads to the base
shear coefficients, at natural period of structural vibration about 1 second, that is close to the counterpart in accordance
with UBC-1997. However, in case of structures with very low periods (less than 1 second), the base shear coefficients in
Zone 1 and Zone 2 are about 20 and 1.3 percent less than those computed from UBC-1997, respectively. In contrast, it is
found that at large periods of vibration (larger than 1 second), the base shear coefficients will be excessive, resulting in
the unnecessary high construction cost.
It could be concluded that using the with soil coefficient (S) of 2.5 and CS value less than or equal to 0.25 for both low- and
high-frequency structures in Bangkok according to the Ministerial Regulation No 49 gives the optimal base shear forces that
are slightly different to those in Zones 1 and 2 of the UBC-1997, while the base shear coefficient remains identical when
the natural period of vibration is at 1 second.