Seismic performance and design guides of asymmetric building structures

Abstract

Aesthetics and functionality requirements have turned most of the building structures to be asymmetric in recent times. These asymmetric structures have demonstrated poor seismic performance while experiencing major earthquakes in the past. Such buildings exhibit complex vibration characteristics under dynamic loads as there is coupling between the lateral and torsional components of vibration, and are referred to as torsionally unbalanced (TU) buildings. Despite the advancement of various analysis and design tools, asymmetric structures tend to fail under seismic events when compared with their regular counterparts. One of the main reasons behind the failure of asymmetric structures is that their behavior is not well understood and the seismic design procedures have only been established considering over-simplified analytical procedures using single storey structures for analytical investigations. The established analytical procedures are, however, not representative of multi-storey structures where the seismic response becomes highly complicated and cannot be accurately estimated. Moreover, the post-earthquake assessments have identified torsional distress at weak locations as the major cause of failure in such structures. Therefore, capturing the accurate seismic response in a multi-storey asymmetric structure is a challenging task for structural engineers as there has been very little research that covers both local damage response and global behavior of asymmetric structures. This eventually demands extensive experimental investigations on a wide range of asymmetric structures as the existing data-stock on experimental investigation of asymmetric structures is insufficient in evaluating both local damage response and global behavior of the asymmetric structures. Therefore, this dissertation is concerned with the damage response investigation of asymmetric structures in terms of local response such as residual strains and global response such as displacements, inter-storey drifts and accelerations along with the dynamic properties of the structure that are useful when correlated with the damage state of the asymmetric structures. The main work presented includes: (1) experimental testing of a plan-asymmetric reinforced concrete (RC) structure for damage evaluation and global response assessment (2) extensive experimental testing of vertical and plan-asymmetric steel structures for damage response simulation and assessment of global behavior of asymmetric structures (3) development of the finite element (FE) model for local and global response validation. Firstly, this dissertation demonstrates the successful implementation of fibre brag grating (FBG) sensors for local response monitoring and evaluation of the state of damage inside the structural components in the plan-asymmetric RC frame shear wall structure. The capability of FBG sensors for damage assessment inside the structural components is ensured by correlating the residual strain data with the variation in the dynamic characteristics of the plan-asymmetric structure and visual inspections. The structure has been transformed from an elastic state to a highly inelastic state by progressively increasing the seismic excitation. The influence of torsional vibrations considering the precise and detailed measurements of varying strain responses and effective estimation of damage response within the structural components along with the global response of the structure has been demonstrated in detail. Secondly, extensive experimental work has been conducted on a wide range of vertical and plan-asymmetric steel structures to simulate and compare the damage behavior for various asymmetric characteristics. For local strain response, bare FBG sensors have been used onto the surface of the structure near flexible side (FS) and stiff side (SS) at all floor levels. For global response, accelerations and rotational drifts have been determined at both FS and SS of the asymmetric structures. These responses were correlated to observe the response transition at each edge of the structure over varying characteristics of irregularities. Besides, it is demonstrated how the interaction of various irregularities influenced the seismic response and made the asymmetric structure vulnerable to damage. Finally, to observe the complex nature of local response and uncertainty associated with the global responses, validated numerical models were established. Based on the cumulative knowledge from the experimental testing and the investigation of FE models, seismic design guidelines are proposed for various asymmetric structures. The research findings can also be used for the advance prediction of the crack monitoring and the critical state of the asymmetric structures. In addition, the detailed contour plots of the local deformation concentration at the FS and SS can be used for the structural health monitoring of the existing asymmetric structures of similar types.

Date of Award	2019
Original language	English