Seismic analysis of multilayered half spaces | |
| Author | Lai, Tao |
| Call Number | AIT Diss. no.ST-96-01 |
| Subject(s) | Earthquake engineering Structural dynamics |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ST-96-01 |
| Abstract | The horizontally stratified ground domain is taken as a multilayered half space and separated into a near field and a far field. Layers may be elastic or viscoelastic of distinct properties. The near field is discretized into finite elements. The far field is discretized into infinite elements; horizontal infinite elements for top layers, and radiating infinite elements for the underlying half space. Far-field displacement functions of three fundamental problems in harmonic vibration are used as the shape functions of infinite element nodal lines; i.e., the first fundamental problem is used on the ground surface, the second in the interior of any homogeneous domain, and the third at the interface between two domains of different properties. The three fundamental problems are; a homogeneous half space, a homogeneous full space, and two different half spaces perfectly bonded together. Each fundamental problem solution is obtained as a linear combination of at the most one surface wave and a finite number of body waves. All such constituent waves are discrete, outgoing and attenuating. The speed, material attenuation, and geometric attenuation of each wave are given explicitly. The modelling has been verified over a wide range of fundamental static and vibration problems. The mass and stiffness matrices of infinite elements involve exponential integrals which are improper. Two schemes are proposed herein; series expansion and optimum backward recurrence. For any order of the integrals, the first scheme and forward recurrence are good for the lower range of the complex argument, while the second scheme is good for the upper range. There is also an intermediate range where all such schemes are valid. Moreover, the Gauss-Laguerre integration is found to yield very accurate results, except for a very small argument of the exponential integrals. The essential harmonic analysis is extended to seismic analysis through the Fast Fourier Transform technique. The near surface wave patterns are generated by three orthogonal fictitious point forces applied underground at a focal point, which is encompassed in the near field . The location of the focal point might be placed right under the site or structure of interest, and its depth could be reasonably assumed. The harmonic analysis yields the Fourier transform of response in terms of the amplitudes of the three orthogonal force components, thus in terms of the Fourier transforms of the accelerations in three orthogonal directions recorded or specified for the ground surface. An appropriate inverse Fourier transform algorithm yields the transient response. The wave patterns near the ground surface can be more refined in case of the availability of simultaneous records at more seismograph stations by introducing more focal points. The validity of this earthquake input algorithm is verified through an actual 'deep and soft' site response analysis, where the responses, generated by a single focal point and two focal points, are presented. The easy applicabilion of this algorithm to soil-structure interaction is demonstrated by considering a cylindrical foundation embedded in a layered half space subjected to earthquake excitations in three directions simultaneously. The effects of inertial force and trenching on the foundation response are also considered. |
| Year | 1996 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ST-96-01 |
| Type | Dissertation |
| School | School of Civil Engineering |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Structural Engineering (STE) /Former Name = Structural Engineering and Construction (ST) |
| Chairperson(s) | Karasudhi, Pisidhi;Wijeyewickrema, Anil C.; |
| Examination Committee(s) | Worsak Kanok-Nukulchai;Pennung Warnitchai;Ashford, Scott A.;Gladwell, G. M. L.; |
| Scholarship Donor(s) | The Government of Japan; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1996 |