PEER Testbed Study on a Laboratory Building: Exercising Seismic Performance Assessment

From 2002 to 2004 (years five and six of a ten-year funding cycle), the PEER Center organized the majority of its research around six testbeds. Two buildings and two bridges, a campus, and a transportation network were selected as case studies to “exercise” the PEER performance-based earthquake engineering methodology. All projects involved interdisciplinary teams of researchers, each producing data to be used by other colleagues in their research. The testbeds demonstrated that it is possible to create the data necessary to populate the PEER performancebased framing equation, linking the hazard analysis, the structural analysis, the development of damage measures, loss analysis, and decision variables. This report describes one of the building testbeds—the UC Science Building. The project was chosen to focus attention on the consequences of losses of laboratory contents, particularly downtime. The UC Science testbed evaluated the earthquake hazard and the structural performance of a well-designed recently built reinforced concrete laboratory building using the OpenSees platform. Researchers conducted shake table tests on samples of critical laboratory contents in order to develop fragility curves used to analyze the probability of losses based on equipment failure. The UC Science testbed undertook an extreme case in performance assessment—linking performance of contents to operational failure. The research shows the interdependence of building structure, systems, and contents in performance assessment, and highlights where further research is needed. The Executive Summary provides a short description of the overall testbed research program, while the main body of the report includes summary chapters from individual researchers. More extensive research reports are cited in the reference section of each chapter

A study on damping ratio of EPS foam filled CFRP composite tubes

This study aims to investigate the damping behavior of the fundamental mode of a foam-filled carbon fibre reinforced polymer composite (CFRP) tube when subjected to base excitations. In particular, expanded polystyrene (EPS) foam balls (with negligible mass) of different sizes are used as fillers in the tube and the enhancement in damping ratio of the fundamental mode w.r.t the empty condition is evaluated for different intensity of base excitation. Shake table tests are performed on cantilever CFRP composite square hollow tube subjected to base excitation with varying amplitudes. The tube is filled with foam balls (of two different sizes) for varying depths of filling (no filling, one-third, two-third, and full). Accelerometers are mounted at different positions along the tube length and at the table to record the accelerations data for evaluation of damping ratio. From the recorded responses, frequency, mode shape and damping ratio of the fundamental mode are evaluated using a well-known approach. The damping ratio is noted to be around 1.41x (times) higher for the completely foam ball (bigger size) filled case under r.m.s base acceleration of 0.3 g when compared with the values corresponding to the empty case. The results suggest that the bigger foam balls enhance the damping ratio significantly without altering the natural frequency owing to additional energy dissipation in friction and impact generated through the sliding and collision of the balls while the tube is in motion

Damage Detection in Railway Truss Bridges Employing Data Sensitivity under Bayesian Framework: A Numerical Investigation

In general, for a structure it is quite difficult to get information about all of its modes through its dynamic response under ambient or external excitation. Therefore, it is vital to exhaustively use the available information in the acquired modal data to detect any damage in the structures. Further, in a Bayesian algorithm, it can be quite beneficial if a damage localization algorithm is first used to localize damage in the structure. In this way, the number of unknown parameters in the Bayesian algorithm can be reduced significantly and thus, the efficiency of Bayesian algorithm can be enhanced. This study exploits a mode shape and its derivative based approach to localize damage in truss type structures. For damage quantification purpose, a parameter sensitivity based prediction error variance approach in Bayesian model updating is employed, which allows extracting maximum information available in the modal data. This work employs the sensitivity based Bayesian algorithm to determine the posterior confidence in truss type railway bridges. Results of the study show that the proposed approach can efficiently detect and quantify damage in railway truss bridges

Stress and Strain Concentration Factors in Orthotropic Composites with Hole under Uniaxial Tension

A systematic investigation is carried out on how different parameters influence stress and strain concentration factors (SCF and SNCF) in a composite plate with a hole under uniaxial tension. Flat and singly curved composite plates have been modelled in ANSYS 15.0. The governing parameter includes: (i) size, shape and eccentricity of hole, (ii) number of plies, (v) fiber orientation and (vi) plate curvature. It is observed that different parameters influence the SCF and SNCF with varying degrees. For example, SCF may be as high as 7.16 for a square shaped hole. Also, SCF and SNCF are found to be approximately same in most of the cases. Finally, simplified design formulas are developed for evaluation of SCF for a wide range of hole size, eccentricity and fiber orientation

Effect of in-plane boundary conditions on elastic buckling behavior of solid and perforated plates

In this work, finite element method is used to obtain elastic buckling loads and mode shapes of plates. The effect of four different in-plane boundary conditions on the elastic buckling load of simply supported plates subjected to in-plane uni-axial compressive loading is studied. Elastic buckling behavior of plates with cut-outs (circular and square with curved corners) is also studied to illustrate the effect of the size, shape and the eccentricity of the cut-out on buckling loads. Results of the study show that the in-plane boundary conditions affect the elastic buckling behavior of the plate to a significant extent. Aspect ratio influences both the mode shape and the elastic buckling load for perforated plates, whereas its influence is generally limited to mode shape only in case of a solid plate. Restraints on the in-plane movements of plate?s unloaded edges have different influence on the elastic buckling behavior of the plate when the position of cut-out is changed along the x-axis (loading direction) and along the y-axis (normal to loading direction) of the plate. Also, results show that a large cut-out in the vicinity of edges makes the plate unstable at a much lower load compared to the plate with no cut-out. It is envisioned that the results of this study may provide insight to predict buckling loads in practical scenarios.by Kanta Prajapat, Samit Ray-Chaudhuri and Ashwini Kuma

A review of stress concentration factors in tubular and non-tubular joints for design of offshore installations

Tubular structures are widely used in offshore installations, trusses, high rise buildings, towers for wind turbines, ski-lift installations, lightning, road pole signals etc., owing to their excellent structural performance and attractive appearance. Stress concentration, especially in the welded joints of these structures, is an important design consideration particularly for fatigue design. In the context of tubular and non-tubular joints, this paper provides a review of the experimental and numerical studies that have been carried out so far to determine the stress concentration factor (SCF). Emphasis is also placed on the complexity of capturing different types of stresses in tubular/non-tubular joints for estimation of SCF. Present code provisions for evaluation of SCF are also discussed. Further, a few issues, which require significant research effort to advance our understanding and to improve the current design guidelines, have been identified