This present issue of Structures and Buildings presents five papers investigating the failure mode, strength and ductility of various structural elements from their research activity originating in Turkey, India, USA, UK and Sweden. The first paper considers numerical and analytical modelling to examine the lateral stability of reinforced-concrete (RC) beams with initial geometric imperfections. The second paper discusses the experimental observations on the axial behaviour of concrete-filled steel tubular (CFST) columns with different cross-sections and two different concrete infills. The third and fourth papers present analytical approaches to examine the structural performance of uncommon steel elements, such as corrugated web steel coupling beams and cast-iron beams exposed to fire. The final paper provides experimental data and empirical expression for the proper design of anchor bolts and washers to avoid brittle failure by splitting of the bottom rail in timber shear walls.
The first paper (Kalkan et al., 2016) extended the previous analytical and experimental studies that examined the lateral stability of RC beams according to initial geometric imperfections, different amount of longitudinal and transverse reinforcements, and elastic–inelastic stress–strain properties of materials. On the basis of the previous analytical models and existing test results, this study developed general buckling moment and lateral deflection equations of RC beams with initial geometric imperfections. The proposed buckling moment equation showed that a sweep equal to the girder sweep tolerance of the Precast/Prestressed Concrete Institute manual corresponds to a reduction of about 35% in the buckling moment compared to the perfect configuration of the beam. Overall, the present study provides reasonable approaches for estimating the buckling moments of RC beams, in particular, with geometrical imperfections and concrete cracking.
The next paper (Sankar Jegadesh and Jayalekshmi, 2016) tested the axial behaviour of CFST columns with different cross-sections (circular, square, and rectangular types) and two different concrete infills produced using fly ash as partial replacement (25%) of cement and 0·5–1·5% polypropylene fibres. A comparative study was also made between the experimental strength and theoretical values obtained from various international design codes. Test results showed that the failure mode of CFST columns depended on their aspect ratio (L/D), indicating the compression failure for L/D ≤ 4, compression and buckling failure for 4 < L/D ≤ 8, and buckling failure for L/D > 8. Furthermore, the axial load-displacement curve revealed that 25% partial replacement of cement by fly ash and 1% addition of fibre in the concrete is advantageous as infill material in CFST columns. Most code equations specified in EC 4, ACI/AS, and BSI provisions conservatively predicted the axial strength of CFST columns, whereas CECS code equation tended to overestimate the strength.
The third paper (Zirakian et al., 2016) examined the application of corrugated webs as an alternative to flat webs having stiffeners for steel coupling beams in lateral force resisting systems. In finite-element models using the general purpose program Ansys 11·0, various parameters related to the web steel coupling beams were investigated as follows: the shape of the web plate including flat, trapezoidal, curved and zigzag patterns; the thickness and number of corrugations; and corrugation angle. Although the demonstration of the introduced finite-element modelling approach was somewhat insufficient, pushover analyses showed that the use of corrugated webs instead of stiffened flat webs can improve the rotation capacity of steel coupling beams, indicating the energy dissipation capabilities of steel coupling beams depends on corrugation parameters. Overall, application of steel beams with trapezoidal, curved and zigzag web forms as coupling elements in coupled shear wall systems is promising in terms of performance and cost.
In the fourth paper, Maraveas et al. (2016) present the development of a simplified method to calculate the flexural capacity of cast iron beams in a jack arched system exposed to a standard ISO 834 fire, on the basis of a strain distribution approach extended from the previous works. In the simplified method, unprotected beams (fire exposure to the entire perimeter of the cross-section) and protected beams (jack arched, with only the bottom flange exposed to fire) were considered. Validation of the method indicated that the proposed simplified method is sufficiently accurate as the basis of a design method. This paper also provides a calculation example for the utilisation factor (the ratio of applied bending moment in fire to the cross-section moment resistance at ambient temperature) for the Armley cross-section.
The final paper (Girhammar and Källsner, 2016) developed a new plastic design method for light-framed timber shear walls to ensure ductile behaviour of the sheathing-to-framing joints and to avoid brittle failure of the bottom rail. This paper also presented experimental results for sheathed bottom rails in light-framed timber shear walls of different geometrical configurations with respect to the anchor bolts. The tests indicate that the failure load of the bottom rail increases with decreasing distance from the edge of the washer to the loaded edge of the bottom rail. Overall, this study emphasised the importance of establishing design approach with respect to splitting failure of the bottom rail.
