Seismic Performance of Steel Frames with Semirigid Connections

The nonlinear stiffness matrix method was incorporated to investigate the structural performance of steel portal frames with semirigid connections. A portal frame with unstiffened extended end-plate connection was designed to demonstrate the adequacy of the proposed method. Besides, the seismic performance of steel portal frames with semirigid connections was investigated through time history analysis where kinematic hysteresis model was assigned to semirigid connections to account for energy dissipation and unloading stiffness. Based on the results of the study, it was found that generally semirigid connections influenced the force distribution which resulted in the decrease in base shear and lighter frame compared to the rigid one. The results also indicated that there was no direct relationship between maximum displacement at the top and connection stiffness in high-rise frames

Evaluation of the efficiency of single-outrigger structural systems in tall buildings

This study investigated the seismic behaviour of the single-outrigger frame systems and proposed the optimum location of outrigger in tall buildings compared to conventional approaches. For this purpose, a pushover analysis was carried out on different forms of the single-outrigger braced high rise buildings to capture the seismic response. An innovative Stiffness Ratio Method (SRM) technique has been utilised for small-scale 3-D modeling using Finite Element Modeling (FEM) in Abaqus/CAE software commercial program. The performance of single-outrigger systems under uniform loading was measured through lateral displacement and drift. The results confirm that by changing an outrigger's position throughout the height of the building, the strength and stiffness will experience significant changes. Placing an outrigger at the top level of the building termed Cap model led to a reduction in lateral drift by 72 percent, while it reached 84 percent, where it placed at 0.4 height of the building hereinafter called Optimal model. Overall, the results showed that the optimal form of the single-outrigger systems' efficiency is 17 percent higher than the conventional model (Cap model) in the reduction of the top displacement of the building under lateral loads

Performance of epoxy resin polymer as self-healing cementitious materials agent in mortar

This research investigated the application of epoxy resin polymer as a self-healing strategy for improving the mechanical and durability properties of cement-based mortar. The epoxy resin was added to the concrete mix at various levels (5, 10, 15, and 20% of cement weight), and the effectiveness of healing was evaluated by microstructural analysis, compressive strength, and non-destructive (ultrasonic pulse velocity) tests. Dry and wet-dry conditions were considered for curing, and for generating artificial cracks, specimens at different curing ages (1 and 6 months) were subjected to compressive testing (50 and 80% of specimen’s ultimate compressive strength). The results indicated that the mechanical properties in the specimen prepared by 10% epoxy resin and cured under wet-dry conditions was higher compared to other specimens. The degree of damage and healing efficiency index of this particular mix design were significantly affected by the healing duration and cracking age. An optimized artificial neural network (ANN) combined with a firefly algorithm was developed to estimate these indexes over the self-healing process. Overall, it was concluded that the epoxy resin polymer has high potential as a mechanical properties self-healing agent in cement-based mortar

Evaluation of mechanical and environmental properties of engineered alkali-activated green mortar

10.3390/ma13184098Materials1318409

Behaviour and design of cold-formed steel C-sections with cover plates under bending

This paper presents an experimental, analytical and numerical investigation on the correlation between non-dimensional slenderness and pure bending strength of stiffened cold-formed steel as a construction material. Cover plates with three different thicknesses (1.6, 2 and 4 mm) were incorporated to evaluate the slenderness effects on flexural performance of C-sections installed at top flanges only as it would be the predicted location for local and distortional buckling. The lateral supports were provided to prevent lateral torsional buckling in the experiment investigation. Application of the Direct Strength Method led to an extensive parametric study to investigate the moment capacity and buckling modes of specimens with different cover plate thicknesses. A nonlinear finite element model was developed and verified against the test results in terms of failure buckling modes. Moreover, a newly recommended non-dimensional slenderness of DSM in order to address the plastic strength for stocky sections was proposed in this paper. The results explicitly showed that the cover plate reduced the non-dimensional slenderness which resulted in improved buckling capacity. Also, it was concluded that the design strengths predicted by the current DSM in accordance with the American specification guideline, AISI, was conservative for sturdy sections as these sections can develop plastic moment

Performance of steel beams strengthened with pultruded CFRP plate under various exposures

The use of Carbon Fiber Reinforced Polymer (CFRP) to strengthen steel structures has attracted the attention of researchers greatly. Previous studies demonstrated bonding of CFRP plates to the steel sections has been a successful method to increase the mechanical properties. However, the main limitation to popular use of steel/CFRP strengthening system is the concern on durability of bonding between steel and CFRP in various environmental conditions. The paper evaluates the performance of I-section steel beams strengthened with pultruded CFRP plate on the bottom flange after exposure to diverse conditions including natural tropical climate, wet/dry cycles, plain water, salt water and acidic solution. Four-point bending tests were performed at specific intervals and the mechanical properties were compared to the control beam. Besides, the ductility of the strengthened beams and distribution of shear stress in adhesive layer were investigated thoroughly. The study found the adhesive layer was the critical part and the performance of the system related directly to its behavior. The highest strength degradation was observed for the beams immersed in salt water around 18% after 8 months exposure. Besides, the ductility of all strengthened beams increased after exposure. A theoretical procedure was employed to model the degradation of epoxy adhesiv