Strength reduction factor for MDOF soil-structure systems

Marshall

2016

Engineering Structures

The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractA comprehensive parametric study has been carried out to investigate the seismic performance of multi-storey shear buildings considering soil-structure interaction (SSI). More than 40,000 SDOF and MDOF models are designed based on different lateral seismic load patterns and target ductility demands to represent a wide range of building structures constructed on shallow foundations. The cone model is adopted to simulate the dynamic behaviour of an elastic homogeneous soil half-space. 1, 5, 10, 15 and 20-storey SSI systems are subjected to three sets of synthetic spectrum-compatible earthquakes corresponding to different soil classes, and the effects of soil stiffness, design lateral load pattern, fundamental period, number of storeys, structure slenderness ratio and site condition are investigated.The results indicate that, in general, SSI can reduce (up to 60%) the strength and ductility demands of multi-storey buildings, especially those with small slenderness ratio and low ductility demands. It is shown that code-specified design lateral load patterns are more suitable for long period flexible-base structures; whereas a trapezoidal design lateral-load pattern can provide the best solution for short period flexible-base structures. Based on the results of this study, a new design factor R F is introduced which is able to capture the reduction of strength of single-degree-of-freedom structures due to the combination of SSI and structural yielding. To take into account multi-degree-of-freedom effects in SSI systems, a new site and interaction-dependent modification factor R M is also proposed. The R F and R M factors are integrated into a novel performance-based design method for site and interaction-dependent seismic design of flexible-base structures. The adequacy of the proposed method is demonstrated through several practical design examples.

Section: Sdof Ductility Reduction Factor R mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Performance-based seismic design of flexible-base multi-storey buildings considering soil–structure interaction

Marshall

2016

Engineering Structures

“…Several studies investigated the effects of SSI on elastic and inelastic response of buildings [19][20][21][22][23][24][25][26][27]. In general, the results of these studies demonstrated that SSI can significantly affect the seismic response of structures located on soft soils by altering the overall stiffness and energy dissipation mechanism of the systems.…”

Section: Introductionmentioning

confidence: 99%

Optimum lateral load distribution for seismic design of nonlinear shear-buildings considering soil-structure interaction

Ganjavi

Soil Dynamics and Earthquake Engineering

Bolourchi

2016

Self Cite

The lateral load distributions specified by seismic design provisions are primarily based on elastic behaviour of fixed-base structures without considering the effects of soil-structure-interaction (SSI).Consequently, such load patterns may not be suitable for seismic design of non-linear flexible-base structures. In this paper, a practical optimization technique is introduced to obtain optimum seismic design loads for non-linear shear-buildings on soft soils based on the concept of uniform damage distribution. SSI effects are taken into account by using the cone model. Over 30,000 optimum load patterns are obtained for 21 earthquake excitations recorded on soft soils to investigate the effects of fundamental period of the structure, number of stories, ductility demand, earthquake excitation, damping ratio, damping model, structural post yield behaviour, soil flexibility and structural aspect ratio on the optimum load patterns.The results indicate that the proposed optimum load patterns can significantly improve the seismic performance of flexible-base buildings on soft soils.

“…The additional mass moment of inertia was attached to the foundation to have a rigid body movement in the rocking degree of freedom in phase with the foundation. Because the above coefficients are frequency independent, an internal rotational degree of freedom φ with a mass moment of inertia m φ was also defined to take into account the soil dynamic‐stiffness frequency dependency . For a specific earthquake, the response of a soil‐structure system is directly affected by the dynamic characteristics of the structure as well as the soil beneath it.…”

Section: Details Of Structure Foundation and Soil Conditionmentioning

confidence: 99%

“…As a step forward, several studies investigated the effects of base flexibility on the seismic response of single‐degree‐of‐freedom (SDOF) and multi‐degree‐of‐freedom (MDOF) systems to include the SSI effects. These investigations were mainly devoted to study the strength–ductility relationship of soil‐structure systems.…”

Section: Introductionmentioning

confidence: 99%

Effects of soil‐structure interaction and lateral design load pattern on performance‐based plastic design of steel moment resisting frames

Ganjavi

Gholamrezatabar²,

Structural Design Tall Build

2019

Self Cite

Summary The effects soil‐structure interaction (SSI) and lateral design load‐pattern are investigated on the seismic response of steel moment‐resisting frames (SMRFs) designed with a performance‐based plastic design (PBPD) method through a comprehensive analytical study on a series of 4‐, 8‐, 12‐, 14‐, and 16‐story models. The cone model is adopted to simulate SSI effects. A set of 20 strong earthquake records are used to examine the effects of different design parameters including fundamental period, design load‐pattern, target ductility, and base flexibility. It is shown that the lateral design load pattern can considerably affect the inelastic strength demands of SSI systems. The best design load patterns are then identified for the selected frames. Although SSI effects are usually ignored in the design of conventional structures, the results indicate that SSI can considerably influence the seismic performance of SMRFs. By increasing the base flexibility, the ductility demand in lower story levels decreases and the maximum demand shifts to the higher stories. The strength reduction factor of SMRFs also reduces by increasing the SSI effects, which implies the fixed‐base assumption may lead to underestimated designs for SSI systems. To address this issue, new ductility‐dependent strength reduction factors are proposed for multistory SMRFs with flexible base conditions.