Dynamic simulation of CFRP strengthened steel column under impact loading

Carbon fibre reinforced polymer (CFRP) strengthening of metallic structures under static loading has shown great potential in the recent years. However, steel structures are often experienced natural (e.g. earthquake, wind) as well as man-made (e.g. vehicular impact, blast) dynamic loading. Therefore, there is a growing interest among the researchers to investigate the capability of CFRP strengthened members under such dynamic conditions. This study focuses on the finite element (FE) numerical modelling and simulation of CFRP strengthened steel column under transverse impact loading to predict the behaviour and failure modes. Impact simulation process and the CFRP strengthened steel column are validated with the existing experimental results in literature. The validated FE model of CFRP strengthened steel column is then further used to investigate the effects of transverse impact loading on its structural performance. The results are presented in terms of transvers e impact force, lateral and axial displacement, and deformed shape to evaluate the effectiveness of CFRP strengthening technique. Comparisons between the bare steel and CFRP strengthened steel columns clearly indicate the performance enhancement of strengthened column under transverse impact loading.

Durability study of CFRP strengthened steel circular hollow section members under marine environment

Galvanic corrosion is a common phenomenon in Carbon Fibre Reinforced Polymer (CFRP) strengthened steel structures in wet environments and submerged conditions, which reduces durability by weakening the bond between the CFRP and steel substrate. CFRP materials have already been proven to have superior resistance to corrosion and chemical attacks but the adhesive and steel are generally affected by long-term exposure to moisture, especially in conjunction with salts resulting from deicing of ocean spray. This paper presents the results of a research program to improve the durability of CFRP strengthened steel circular hollow section (CHS) members by treating the steel surface with an epoxy based adhesion promoter and inserting Glass Fibre Reinforced Polymer (GFRP) as a galvanic corrosion barrier against simulated sea water. It also presents the effects of accelerated corrosion on the bond of CFRP strengthened hollow steel members. The program consisted of four CFRP strengthened steel beams and one unstrengthened steel beam. Two strengthened beams were used as control while the other two beams were exposed to a highly corrosive environment to induce accelerated corrosion. The corrosion rate was considered 10% which represents a moderate level of loss in the cross-sectional area of the steel tube throughout its intended service life. The beams were then loaded to failure under four-point bending. The research findings indicate that the accelerated corrosion adversely affected the ultimate strength of the conditioned beams and the embedded glass fibre enhanced the bond durability.

Bacterial adherence and biofilm formation on medical implants : a review

Biofilms are a complex group of microbial cells that adhere to the exopolysaccharide matrix present on the surface of medical devices. Biofilm-associated infections in the medical devices pose a serious problem to the public health and adversely affect the function of the device. Medical implants used in oral and orthopedic surgery are fabricated using alloys such as stainless steel and titanium. The biological behavior, such as osseointegration and its antibacterial activity, essentially depends on both the chemical composition and the morphology of the surface of the device. Surface treatment of medical implants by various physical and chemical techniques are attempted in order to improve their surface properties so as to facilitate bio-integration and prevent bacterial adhesion. The potential source of infection of the surrounding tissue and antimicrobial strategies are from bacteria adherent to or in a biofilm on the implant which should prevent both biofilm formation and tissue colonization. This article provides an overview of bacterial biofilm formation and methods adopted for the inhibition of bacterial adhesion on medical implants

Improving the teaching and learning of steel structural design

Engineering students are best able to understand theory when one explains it in relation to realistic problems and its practical applications. Teaching theory in isolation has led to lower levels of comprehension and motivation and a correspondingly higher rate of failure. At Queensland University of Technology, a number of new methods have been introduced recently to improve the teaching and learning of steel structural design at undergradt1ate level. In the basic steel structures subject a project-based teaching method was introduced in which the students were required to analyse, design and build the lightest I most efficient steel columns for a given target capacity. A design assignment involving simple, but real structures was also introduced in the basic steel structures subject. Both these exercises simulated realistic engineering problems from the early years of the course and produced a range of benefits. Improvements to the teaching and learning was also made through integration of a number of related structural engineering subjects and by the introduction of animated computer models and laboratory models. This paper presents the details of all these innovative methods which improved greatly the students' understanding of the steel structures design process.

Behaviour of corrugated steel roof cladding under combined wind uplift and racking

During high wind events, crest-fixed profiled steel roof claddings in low-rise buildings can be subjected to combined cyclic wind uplift and in-plane racking (shear) forces. Static and cyclic tests of corrugated steel roof claddings were carried out to investigate the effect of in-plane racking force on the uplift strength, in particular, in relation to the fatigue cracking commonly observed under cyclic wind uplift. The presence of racking force appeared to have insignificant effect on the static and cyclic wind uplift strength. It may therefore be possible to include the diaphragm strength of these claddings in the design of low-rise buildings in a similar manner to valley-fixed claddings. This may lead to a reduction in bracing requirements.

Profiled steel roof claddings under high wind forces

Profiled steel roof claddings in Australia and its neighbouring countries are commonly made of very thin high tensile steel and are crest-fixed intermittently with screw fasteners. The failure of the roof cladding systems was due to a local failure (dimpling of crests I pull-through) at the fasteners under wind uplift Cyclic wind uplift during cyclones causes fatigue cracking to occur at the fastener holes which leads to pull-through failures at lower load levels. At present the design of these claddings is entirely based on testing. In order to improve the understanding of the behaviour and the design and test methods of these claddings under wind uplift loading during storms and cyclones, a detailed investigation consisting of finite element analyses, static and fatigue experiments and cyclonic wind modelling was carried out on two-span roofing assemblies of three common roofing profiles. This paper presents the details of this investigation and its important results.

Experimental Study of crack propagation in carbon steel using acoustic emission

Acoustic emission technique has become a significant and powerful structural health monitoring tool for structures. Researches to date have been done on crack location, fatigue crack propagation in materials and severity assessment of failure using acoustic emission technique. Determining severity of failure in steel structures using acoustic emission technique is still a challenge to accurately determine the relationship between the severity of crack propagation and acoustic emission activities. In this study three point bending test on low carbon steel samples along with acoustic emission technique have been used to determine crack propagation and severity. A notch is introduced at the tension face of the loading point to the samples to initiate the crack. The results show that the percentage of load drop of the steel specimen has a reciprocal relationship with the crack opening i.e. crack opening zones are influenced by the loading rate. In post yielding region, common acoustic emission signal parameters such as, signal strength, energy and amplitudes are found to be higher than those at pre-yielding and at yielding.

Experimental studies of cold-formed steel hollow section columns at elevated temperatures

This paper reports the details of an experimental study of cold-formed steel hollow section columns at ambient and elevated temperatures. In this study the global buckling behaviour of cold-formed Square Hollow Section (SHS) slender columns under axial compression was investigated at various uniform elevated temperatures up to 700℃. The results of these column tests are reported in this paper, which include the buckling/failure modes at elevated temperatures, and ultimate load versus temperature curves. Finite element models of tested columns were also developed and their behaviour and ultimate capacities at ambient and elevated temperatures were studied. Fire design rules given in European and American standards including the Direct Strength Method (DSM) based design rules were used to predict the ultimate capacities of tested columns at elevated temperatures. Elevated temperature mechanical properties and stress-strain models given in European steel design standards and past researches were used with design rules and finite element models to investigate their effects on SHS column capacities. Comparisons of column capacities from tests and finite element analyses with those predicted by current design rules were used to determine the accuracy of currently available column design rules in predicting the capacities of SHS columns at elevated temperatures and the need to use appropriate elevated temperature material stress-strain models. This paper presents the important findings derived from the comparisons of these column capacities.

Web crippling tests of cold-formed steel channels under two flange load cases

Cold-formed steel members have many advantages over hot-rolled steel members. However, they are susceptible to various buckling modes at stresses below the yield stress of the member because of their relatively high width-to-thickness ratio. Web crippling is a form of localized failure mode that can occur when the members are subjected to transverse high concentrated loadings and/or reactions. The four common loading conditions are the end-one-flange (EOF), interior-one-flange (IOF), end-two-flange (ETF) and interior-two-flange (ITF) loadings. Recently a test method has been proposed by AISI to obtain the web crippling capacities under these four loading conditions. Using this test method 42 tests were conducted in this research to investigate the web crippling behaviour and strengths of unlipped channels with stocky webs under ETF and ITF cases. DuraGal sections having a nominal yield stress of 450 MPa were tested with different web slenderness and bearing lengths. The flanges of these channel sections were not fastened to the supports. In this research the suitability of the currently available design rules for unlipped channels subject to web crippling was investigated, and suitable modifications were proposed where necessary. In addition to this, a new design rule was proposed based on the direct strength method to predict the web crippling capacities of tested beams. This paper presents the details of this experimental study and the results.

Local buckling studies of cold-formed steel compression members at elevated temperatures

Cold-formed steel members have been widely used in residential and commercial buildings as primary load bearing structural elements. They are often made of thin steel sheets and hence they are more susceptible to local buckling. The buckling behaviour of cold-formed steel compression members under fire conditions is not fully investigated yet and hence there is a lack of knowledge on the fire performance of cold-formed steel compression members. Current cold-formed steel design standards do not provide adequate design guidelines for the fire design of cold-formed steel compression members. Therefore a research project based on extensive experimental and numerical studies was undertaken to investigate the local buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. First a series of 91 local buckling tests was conducted at ambient and uniform elevated temperatures up to 700oC on cold-formed lipped and unlipped channels. Suitable finite element models were then developed to simulate the behaviour of tested columns and were validated using test results. All the ultimate load capacity results for local buckling were compared with the predictions from the available design rules based on AS/NZS 4600, BS 5950 Part 5, Eurocode 3 Parts 1.2 and 1.3 and the direct strength method (DSM), based on which suitable recommendations have been made for the fire design of cold-formed steel compression members subject to local buckling at uniform elevated temperatures.

Mechanical behavior of circular and square concrete filled steel tube stub columns under local compression

This paper presents a combined experimental and numerical study on the behaviour of both circular and square concrete-filled steel tube (CFT) stub columns under local compression. Twelve circular and eight square CFT stub columns were tested to study their bearing capacity and the key influential parameters. A 3D finite element model was established for simulation and parametric study to investigate the structural behaviour of the stub columns. The numerical results agreed well with the experimental results. In addition, analytical formulas were proposed to calculate the load bearing capacity of CFT stub columns under local compression.

Pull-through failure tests of thin steel roof battens under wind uplift load

Thin profiled steel roof sheeting and battens are increasingly used in the construction of roofing systems of residential, commercial, industrial and farm buildings in Australia. The critical load combination of external wind suction and internal wind pressures that occur during high wind events such as thunderstorms and tropical cylcones often dislocate the roofing systems partially or even completely due to premature roof connection failures. Past wind damage investigations have shown that roof sheeting failures occured at their screw connections to battens. In most of these cases, the screw fastener head pulled through the thin roof sheeting whilst the screw fasteners also pulled out from the battens. Research studis undertaken on the roof sheeting to batten connection failures have improved this situation. However, the batten to rafter or truss connections have not been investigated adequately. Failure of these connections can cause the failure of the entire roof structure as observed during the recent high wind events. Therefore a detailed experimental study consisting of both small scale and full scale tests has been undertaken to investigate the steel roof batten pull-through failures in relation to many critical parameters such as steel batten geometry, thickness and grade, screw fastener head sizes and screw tightening. This paper presents the details of this experimental study and the pull-through failure load results obtained from them. Finally it discusses the development of suitable design rules that can be used to determine the pull-through connection capacities of thin steel roof battens under wind uplift loads.

Numerical modeling of thin steel roof battens under wind uplift loads

Extreme wind events such as tropical cyclones, tornadoes and storms are more likely to impact the Australian coastal regions due to possible climate changes. Such events can be extremely destructive to building structures, in particular, low-rise buildings with lightweight roofing systems that are commonly made of thin steel roofing sheets and battens. Large wind uplift loads that act on the roofs during high wind events often cause premature roof connection failures. Recent wind damage investigations have shown that roof failures have mostly occurred at the batten to rafter or truss screw connections. In most of these cases, the screw fastener heads pulled through the bottom flanges of thin steel roof battens. This roof connection failure is very critical as both roofing sheets and battens will be lost during the high wind events. Hence, a research study was conducted to investigate this critical pull-through failure using both experimental and numerical methods. This paper presents the details of numerical modeling and the results.