Nimal Perera

Cyclic behaviour of concrete filled steel tubular column to steel beam connections

An experimental investigation into the behaviour of composite column-to-beam connections using ten large-scale connections has been conducted, four under monotonic loading and six under cyclic loading. This paper presents the details and results of the six cyclic tests. Details and results from the monotonic tests are reported in a companion paper. All connections consisted of a concrete-filled steel tube (CFST) column (circular), a compact universal beam section and a shop fabricated connection stub. Monotonic testing was first carried out and the results, were used to conduct the cyclic tests. Each specimen tested cyclically had the same general form, consisting of a direct connection of the beam to the tube wall (using flange connection plates, and web cleat plates) and reinforcing bars welded to the top and bottom flanges, embedded into the concrete core. It was found that provided the connection to the face of the column had the capacity to force the hinge into the beam itself, the specimen behaved in a very stable fashion, and achieved ductility levels which were only limited by the beam and the nature of the test itself.

Seismic response of building structures with dampers in shear walls

Abstract When buildings are subjected to earthquakes, it is imperative to dissipate some of the input energy through pre-determined and well designed mechanisms. This study investigates the influence of mechanical control on structural systems through the application of strategically located component elements with reliable damping and stiffness properties that can modulate the response. The effects of installing such damping elements at two particular locations have been investigated. These positions are between the shear walls near the coupling beams and within cut out sections of the wall elements in multi-storey structures. Finite element time history analysis is used in the study and results indicate that the proposed procedure is able to achieve reasonable improvements in seismic response.

Monotonic Behaviour of Composite Column to Beam Connections

An experimental investigation into the behaviour of composite column-to-beam connections using ten large-scale connections has been conducted, four under monotonic loading and six under cyclic loading. This paper presents the details and results of the four preliminary monotonic tests. Details and results of the cyclic tests are reported in a companion paper. All connections consisted of a circular concrete-filled steel tubular column, a compact universal beam section and a shop fabricated connection stub. It is a direct connection of the beam to the tube wall (using flange connection plates, and web cleat plates) and four straight reinforcing bars welded to the top and bottom flanges and embedded into the concrete core. It was found that the connection strength increased as the capacity of the embedded bars increased, to a stage where no connection failure occurred, and the beam formed a plastic hinge outside the zone of influence of the bars. The bars were very effective in transferring both compressive and tensile loads directly into the column, and connection behaviour in terms of strength and stiffness was adequate to classify it as a rigid connection.

Human Activity-Induced Vibration in Slender Structural Systems

Abstract Human activity-induced vibrations in slender structural systems become apparent in many different excitation modes and consequent action effects that cause discomfort to occupants, crowd panic and damage to public infrastructure. Resulting loss of public confidence in safety of structures, economic losses, cost of retrofit and repairs can be significant. Advanced computational and visualisation techniques enable engineers and architects to evolve bold and innovative structural forms, very often without precedence. New composite and hybrid materials that are making their presence in structural systems lack historical evidence of satisfactory performance over anticipated design life. These structural systems are susceptible to multi-modal and coupled excitation that are very complex and have inadequate design guidance in the present codes and good practice guides. Many incidents of amplified resonant response have been reported in buildings, footbridges, stadia and other crowded structures with adverse consequences. As a result, attenuation of human-induced vibration of innovative and slender structural systems very often requires special studies during the design process. Dynamic activities possess variable characteristics and thereby induce complex responses in structures that are sensitive to parametric variations. Rigorous analytical techniques are available for investigation of such complex actions and responses to produce acceptable performance in structural systems. This paper presents an overview and a critique of existing code provisions for human-induced vibration followed by studies on the performance of three contrasting structural systems that exhibit complex vibration. The dynamic responses of these systems under human-induced vibrations have been carried out using experimentally validated computer simulation techniques. The outcomes of these studies will have engineering applications for safe and sustainable structures and a basis for developing design guidance.

Dynamic Response of a Rollover Protective Structure

Roll Over Protective Structures (ROPS) are safety devices fitted to heavy vehicles to provide protection to the operator during an accidental roll over. At present, ROPS design standards require full scale destructive testing which can be expensive, time consuming and unsuitable for small companies. More economical analytical methods are not permitted due to a lack of understanding on post yield behaviour and energy absorption capacity of ROPS. With this in mind, a research project was carried out to comprehensively investigate ROPS behaviour using analytical techniques supported by experiments. This paper presents the dynamic impact analysis of a bulldozer ROPS using calibrated finite element models. Results indicate that (i) ROPS posts have significant influence on the energy absorbing capacity,(ii) dynamic amplifications in energy could be up to 25% and (iii) stiffer ROPS cause high peak decelerations that may be detrimental to the operator. The feasibility of using analytical techniques for evaluating ROPS performance has also been demonstrated.

Shear-Critical Impact Response of Biaxially Loaded Reinforced Concrete Circular Columns

A study on the vulnerability of biaxially loaded reinforced concrete (RC) circular columns in multi-story buildings under low- to medium-velocity impacts at shear-critical locations is presented. The study is based on a previously validated nonlinear explicit dynamic finite element (FE) modeling technique developed by the authors. The impact is simulated using force pulses generated from full-scale vehicle impact tests abundantly found in the literature with a view to quantifying the sensitivity of the design parameters of the RC columns under the typical impacts that are representative of the general vehicle population. The design parameters considered include the diameter and height of the column, the vertical steel ratio, the concrete grade, and the confinement effects. From the results of the simulations, empirical equations to quantify the critical impulses for the simplified design of the short, circular RC columns under the risk of shear-critical impacts are developed.

Influence of Structural Sealant Joints on the Blast Performance of Laminated Glass Panels

AbstractThis paper investigates the influence of structural sealant joints on the blast performance of laminated glass (LG) panels, using a comprehensive numerical procedure. A parametric study was carried out by varying the width, thickness, and the Young’s modulus (E) of the structural silicone sealant joints, and the behavior of the LG panel was studied under two different blast loads. Results show that these parameters influence the blast response of LG panels, especially under the higher blast load. Sealant joints that are thicker, have smaller widths, and lower E values increase the flexibility at the supports, and hence increase the energy absorption of the LG panel while reducing the support reactions. Results also confirmed that sealant joints designed according to current standards perform well under blast loads. Modeling techniques presented in this paper could be used to complement and supplement the guidance in existing design standards. The new information generated in this paper will contri...

Design Guidance for Blast-Resistant Glazing

This paper reviews current design standards and test methods for blast-resistant glazing design and compares a typical design outcome with that from comprehensive finite-element (FE) analysis. Design standards are conservative and are limited to the design of relatively small glazed panels. Standard test methods are expensive, create environmental pollution, and can classify the hazard ratings of only smaller glazed panels. Here the design of a laminated glass (LG) panel is carried out according to an existing design standard, and then its performance is examined using comprehensive FE modeling and analysis. Finite-element results indicate that both glass panes crack, the interlayer yields with little damage, and the sealant joints do not fail for the designed blast load. This failure pattern satisfies some of the requirements for minimal hazard rating in the design standard. It is evident that interlayer thickness and material properties are important during the post-crack stage of an LG panel, but they are not accounted for in the design standards. The new information generated in this paper will contribute toward an enhanced blast design of LG panels.

Protection of structural systems and mechanisms from catastrophic and life-threatening failure caused by unforeseeable events

Structural framing systems and mechanisms designed for normal use rarely possess adequate robustness to withstand the effects of large impacts, blasts and extreme earthquakes that have been experienced in recent times. Robustness is the property of systems that enables them to survive unforeseen or unusual circumstances (Knoll and Vogel, 2009). Queensland University of Technology with industry collaboration is engaged in a program of research that commenced 15 years ago to study the impact of such unforeseeable phenomena and investigate methods of improving robustness and safety with protective mechanisms embedded or designed in structural systems. This paper highlights some of the research pertaining to seismic protection of building structures, rollover protective structures and effects of vehicular impact and blast on key elements in structures that could propagate catastrophic and disproportionate collapse.

Health Monitoring of Buildings during Construction and Service Stages Using Vibration Characteristics

Columns and walls in buildings are subjected to a number of load increments during the construction and service stages. The combination of these load increments and poor quality construction can cause defects in these structural components. In addition, defects can also occur due to accidental or deliberate actions by users of the building during construction and service stages. Such defects should be detected early so that remedial measures can be taken to improve life time serviceability and performance of the building. This paper uses micro and macro model upgrading methods during construction and service stages of a building based on the mass and stiffness changes to develop a comprehensive procedure for locating and detecting defects in columns and walls of buildings. Capabilities of the procedure are illustrated through examples.