Development and testing of hybrid precast concrete beam-to-column connections under cyclic loading

In general, precast concrete structure has insufficient ductility to resist seismic load. Detailed understanding on the behaviour of precast concrete connections are limited and current researches are focused addressing this. In this study, two precast and two monolithic concrete joints for exterior beam-to-column connection were tested under cyclic loading. The installation of precast specimens was prepared using dry type method while the monolithic joints were casted in-situ. The evaluation of seismic performance of the joints was conducted by applying hysteretic reverse cyclic loading until failure. Information regarding the strength, ductility and stiffness properties of the connection were recorded and analysed. Based on the test results and damage condition, the initial design of the joint was improved. Consequently, a new joint was constructed and tested, which exhibited a better performance. Precast concrete connections showed stable load–displacement cycles and dissipated a higher energy. The structural drift obtained was up to 9.0%. Pinching and deterioration were attained at a drift ratio of 4.5%. Also, there was improvement in the tested precast joints based on deflection, plastic hinges, crack pattern and shear deformation. Thus, the precast joints had a satisfactory resistance to seismic loads

Shear strengthening of steel I-beams by using CFRP strips

Normally, carbon fiber reinforced polymer (CFRP) strips have been used for flexural strengthening of steel beams, but in this research, application of CFRP strips as shear reinforcements was innovated. In this novel method, investigation on the requirement of applying CFRP on one or both sides of the web, and using different values of CFRP area on the web were the two main objectives. In this research, five specimens were selected. The first specimen (B1) was not strengthened. The second and third beams (B2 and B3) were upgraded on both sides of web with the CFRP ratios of 0.72 and 0.48, respectively. The fourth and fifth specimens (B4 and B5) were strengthened on one side of web with the CFRP ratios of 0.72 and 0.48, respectively. Both numerical simulation and experimental test were used in this research. The results show that by using CFRP strips on web, could appropriately increased the load bearing capacity up to 51. Also, the CFRP ratios of 0.72 and 0.48 for both sides of web have produced the same load capacity. Using less CFRP in the shear zone with the same load capacity of the steel I-beams was one of the significant achievements of this research

Investigation on end anchoring of CFRP strengthened steel I-beams

Problems that frequently occur in carbon fibre reinforced polymer (CFRP) flexural strengthened steel structures include the peeling and debonding at the tip of the CFRP plate. This paper presents a study on the effectiveness of using steel plates and bolts as end-anchors to address these problems. Four steel I-beams were tested to failure. The first specimen was not strengthened and was used as the control beam. The second beam was strengthened with a CFRP plate without any end-anchoring. The third and fourth specimens were strengthened and end-anchored using steel plates and bolts. The number of bolts was the same, however, the length of the steel anchor plates was varied. The beams were tested under four point loads and loaded incrementally while the deflection and strain readings on the critical parts of the beams were recorded. For the numerical study, full three dimensional (3D) simulation and nonlinear static analysis was carried out using ANSYS software. The results indicate that the anchored beams had higher load capacities of up to 24 compared to the non-strengthened beam. End-anchoring with closer bolt spacing was more effective. Both experimental and numerical results are in good agreement highlighting the accuracy of the developed numerical model

Modelling of beam-to-column connections at elevated temperature using the component method

In this paper, a nonlinear model is developed using the component method in order to represent the response of steel connections under various loading conditions and temperature variations. The model is capable of depicting the behaviour of a number of typical connection types including endplate forms (extended and flush) and angle Configurations (double web, top and seat, and combined top-seat-web) in both steel and composite framed structures. The implementation is undertaken within the finite element program ADAPTIC, which accounts for material and geometric nonlinearities. Verification of the proposed connection model is carried out by comparing analytical Simulations with available results of isolated joint tests for the ambient case, and isolated Joint as well as sub-frame tests for elevated temperature conditions. The findings illustrate the reliability and efficiency of the proposed model in capturing the stiffness and strength properties of connections, hence highlighting the adequacy of the component approach in simulating the overall joint behaviour at elevated temperature

The safety performance of guardrail systems: review and analysis of crash tests data

The last decade has witnessed an increased number of vehicles and increased vehicle speed on roads such that the frequency and severity of run-off roadway accidents has increased dramatically. Evaluation of guardrail system performance as an element of providing a safe environment for vehicles and to reduce occupant injuries is deemed to be vital issue. Hence, this paper is going to assess deflection and vehicle trajectory of current guardrail systems. For this purpose, the results of full-scale crash tests for different types of guardrail system are collected from previous crash tests available in the literature. The results showed that for Test 3-11 (according to NCHRP Report 350) with similar post spacing (1905 mm), the trend of vehicle exit speed declined while guardrail maximum permanent deflection increased. In addition, among all system types, guardrail with curb and Thrie-beam guardrail systems were subjected to the lowest amount of deflection although Thrie-beam guardrail was subjected to higher average values for both vehicle exit speed and exit angle. Further, weak-post guardrail system showed to have the highest maximum dynamic and permanent deformation compared to other systems whereas it caused the lowest exit angle to the vehicles

FE modelling of the flexural behaviour of square and rectangular steel tubes filled with normal and high strength concrete

In this research, numerical investigations were carried out to study the behaviour of concrete filled steel tubes having square or rectangular cross-sections. Separate models were used for both normal strength concrete and high strength concrete. More than 50 experimental results were used to verify the FE model and it was found that the FE model accurately predicts the load-deflection curve and ultimate moment capacity of the Concrete filled steel tube (CFST) beams. Thereafter, a parametric study was carried out to evaluate the effect of depth-to-thickness ratio (20−200), compressive strength of infilled concrete (2–100 MPa), shear span-to-depth ratio (1–8), depth-to-width ratio (0.6–2), and yield strength of steel tube (380–490 MPa) on the flexural behaviour of square and rectangular CFST members. It was found that the depth-to-thickness ratio, yield strength of steel and height-to-width ratio has significant effect on the ultimate capacity of CFST beams. The effect of shear span-to-depth ratio and strength of infilled concrete was found to be marginal. Finally, the results of parametric study and experimental data available in literature were used to check the accuracy of the existing design methods presented in EC4 (2004), CIDECT, AISC (2010) and GB50936 (2014). From comparison, it was found that GB50936 (2014) was more accurate but unsafe for low strength infilled concrete. For all cases, EC 4 (2004) was found to be safe and hence is recommended

Performance of CFRP strengthened full-scale SHS connections subjected to cyclic loading

Square hollow section (SHS) beam–column connections are prevalent in steel structures and extensively used in high seismic risk regions due to their significant architectural and structural benefits. Rehabilitation and strengthening of SHS connections are important considerations due to the vulnerable effects of cyclic loading. Studies on the structural performance of CFRP strengthened SHS connections under large displacement cyclic loading are, however, very limited and the finite element (FE) modelling numerical approach not yet been developed. The objective of the current research is to develop a FE modelling numerical approach to simulate the cyclic response of CFRP strengthened SHS beam–column connections. The modelling techniques are validated by comparing the FE model simulated results with the authors’ experimental results. A detailed parametric study is then conducted to study the effects of the thickness of the beam and column section, moment arm, and the strengthening scheme on the cyclic performance of CFRP strengthened SHS beam–column connections. CFRP strengthened SHS beam–column connections have shown improvements in structural performance with respect to moment hysteresis response, stiffness and energy dissipation capacity. Moreover, CFRP strengthened connections showed less tendency for buckling compared to their bare counterparts. Research findings of the present study will be beneficial to restore the structural integrity of SHS beam–column connections through CFRP strengthening.T. Tafsirojjaman, David P. Thambiratnam, N.H. Ramli Sulong, Sabrina Fawzi

Influences of flame-retardant fillers on fire protection and mechanical properties of intumescent coatings

A combination of acrylic binder and flame-retardant ingredients was used to synthesize the solvent-borne intumescent coatings designed for steel substrates. The influences of individual and various combinations of flame-retardant fillers on the fire protection and mechanical properties of the coatings were characterized by using Bunsen burner, thermogravimetric analysis, limiting oxygen index, field emission scanning electron microscopy, freeze thaw cycles, static immersion and pull-off type equipment. It was found that the combination of aluminium hydroxide (Al(OH)(3)) and titanium dioxide (TiO2) has significantly improved the fire protection, thermal stability and water resistance of the coating. This formulation had an LOI value of 34, which indicated good flammability resistance of the coating. The adhesion strength tests showed that the coating added with magnesium hydroxide (Mg(OH)(2)) exhibited maximum bonding strength to the metal surface due to its effective interface adhesion. Hence, the findings from this study revealed that the selection of appropriate combinations of flame-retardant fillers strongly influenced the physical and chemical properties of the coatings. (C) 2014 Elsevier B.V. All rights reserved