This study evaluated the effects of flange thickness to depth of web ratio at three levels (1:2, 1.5:3.5 and 2:5) as well as thickness to depth of web ratio at three levels (0.5:2, 0.5:3.5 and 0.5:5) and width of flange at three levels (3, 3.8 and 4.6 cm) as independent variables on some mechanical properties e.g. modulus of rupture (MOR) and modulus of elasticity (MOE) of I-joist manufactured from ash wood (Fraxinus sp.). For this purpose, response surface methodology (RSM) was applied to evaluate the effects of independent variables on MOR and MOE of I-joist based on a three-level, three-variable central composite rotatable design (CCRD). In this survey, bending test was done according to the ASTM D-5055. Mathematical model equations were derived from computer simulation programing to find significant differences and the most effective variables. According to the results, predicted values were found to be in agreement with actual values (R2 values of 0.99 and 0.98 for MOR and MOE, respectively). The study showed that RSM can efficiently be applied in modeling bending properties of I-joist. It was found that all independent variables had direct effect and significant effect on responces; in a way that flange thickness to depth of web ratio, thickness to depth of beam web ratio and width of flange maintained the MOR and MOE at maximum levels up to 2:5, 0.5:5 and 4.6cm, respectively. Simultaneously, some quadratic and interaction terms of variables had significant effects, too. Generally, increment in flange thickness to depth of web ratio, thickness to depth of web ratio and width of flange increased MOR and MOE of I-joist. Besides, flange thickness to depth of web ratio had the strongest effect on bending strength of beams

Bending strength of I-joist lightened via two methods of crinkleing and honeycombing using poplar species (Popolus deltoids) and eucalyptus (Eucalyptus spp) was studied. Investigated variables consisted of: a) type of flange, b) configuration of lightened core layer in web and c) thermal-pressure treatment surface layers of web. Flange type at two levels: 1) LVL from poplar wood and 2) eucalyptus massive wood, configuration of web core layer at two level too: 1) crinkle and 2) honeycomb and type of treatment applied on surface layers of web which were prepared from poplar layies with 3 mm thick at two levels: 1) thrmo-compressed treated and 2) untreated veneers were selected. Mechanical properties of beam consisted of modulus of rapture (MOR) and modulus of elasticity (MOE) were selected and tested as dependent variables. Obtained results were analyzed in full factorial plot, statistically. After determination of results significance results, means of values were classified by Duncan Multiple Range Test (DMRT). Results showed that using LVL from poplar unlike its low density had higher MOR and MOE values compared with eucalyptuse massive wood. Besides, in order to lighten beam, using honeycomb configuration in web core layer gave more strength to beam in comparison with crinkle configuration. Treatment of surface layers of web had not effect on bending strength, statistically.

In the precast structures, optimization of structural elements is of great interest mainly due to a more rationalized way that elements are produced. There are several elements of precast prestressed concrete that are objects of study in optimization processes, as the prestressed joist applied in buildings slabs. This article inquires into cost minimization of continuous and simply supported slabs, formed by unialveolar beams and prestressed joist, using Genetic Algorithms (GAs). Comparative analyses of the final costs were made for these two precast elements, previously investigated in Castilho [1] and Castilho [2]. Furthermore, parcels of cost function were analyzed for the cases of prestressed joist and unialveolar beam, and the results show that the production stage of the element matches the largest part of the cost function. Also, although the prestressed joist is more economical, unialveolar beam reaches the market to compete with the other precast elements for slabs.

With growth the construction technologies, Cold-Formed Steel, CFS, sections are widely used in ordinary steel buildings because of some advantages such as light weight, ease of installation, decrease in cost, and increase in speed of operation. Using the bolted connections for CFS joist is one of the best details for steel structures.  The main objective of this study is to conduct an experimental research to evaluate the load carrying capacity of bolted connections based on various bolts arrangement. Ten full scale joist-beam connections are tested under the incremental gravity load. The variable parameters are the arrangement of bolts, and thickness of CFS sheets. The joist sections made of two C-shaped, which are back-to-back connected using self-drilling screw bolts in the web. The arrangement of bolts connection and steel sheet thickness are considered as two major factors to improve the load carrying capacity. Base on the obtained results, it was observed that increasing the number of the bolts and their spacing from the neutral axes led to the additional load carrying capacity. Furthermore, it can be concluded that the thickness of CFS sheets play an effective role for load carrying capacity of connections.

In construction of concrete floors, parts of the formwork are sometimes left in place as permanent structural elements. This is to achieve a more straightforward installation procedure and to minimize the future under deck form removal. The present research work deals with, an innovative floor system consisting of hollow-tiles and steel joists. In a hollow-tile floor system, gravity loads are transferred by the slab sitting on top of the blocks to the one way joist and then to the main beams. With the proposed new system the width of the hollow block is doubled so, it is relatively lighter than an ordinary hollow-tile floor system. The joists height is slightly bigger than that in an ordinary hollow-tile floor system; however, the hollow block height remains the same. Thin plastofoams sheets are placed on top of the blocks to fill the gap. During the construction, the fresh concrete weight is carried by temporary vertical posts. After removal of temporary posts, the service loads are transferred to the T beams. This paper provides details for the application of the proposed new floor system in a steel frame building under gravity and quasi static earthquake loading. Various spans and floor thicknesses have been examined and the details are presented.

Analytical solutions based on general differential equations and finite element formulationsfor in-plane analysis of composite steel/concrete beams including the effects of partialinteraction are presented in this study. The partial shear interaction, which happens as aresult of having flexible shear connections, brings about lower flexural rigidities,particularly in hogging regions of the composite beams. The presented analytical solutioncan be used to calculate the in-plane critical stress resultants that may initiate the out-ofplane buckling of the steel joist. Unlike the published works, the current finite elementmodel accommodates the partial shear interaction and general loading and end supportconditions, and also accounts for the variation of beam’s flexural rigidities in hogging andsagging regions. Numerical examples are provided to demonstrate the accuracy, efficiencyand versatility of the derivations.

Composite prestressed joist floors are one of the economical roof systems, which are increasingly used in Iran. In this research, the composite behavior of prestressed joists in composite joist floors has been experimentally evaluated. What can prevent the composite behavior of the prestressed joist and the in-situ concrete slab is the lack of proper transfer of horizontal shear at the contact surface of the prestressed joist and the in-situ concrete. In prestressed joist floors, unlike truss joist floors, it is difficult to install horizontal shear reinforcement between precast and in-situ concrete. This research was carried out in two stages and in each stage the final load as well as the cracking load and moment were evaluated. In the first stage, two prestressed joist samples were tested and the quality of the joists was ensured by matching the laboratory results and the calculated values. In the next stage, samples of composite joist slabs without horizontal shear reinforcement and with the proposed shear reinforcements were made and tested in the laboratory. Based on the results, the slab samples without shear reinforcement were able to resist the fast laboratory loading up to the calculated load based on the bending strength, but they almost immediately suffered brittle failure due to horizontal shear slip, which makes their use under long-term loading in the structure problematic. The proposed reinforcements were able to improve the composite behavior of the joist and in-situ concrete by improving the horizontal shear strength and improve the bearing capacity of the slab up to 27 percent.

The progressive collapse of the 16-story Plasco steel building induced by fire in Tehran on 19 January 2017 led to the death of dozens of firefighters. This paper presents the results of a comprehensive 3D nonlinear finite element analysis of a floor of the Plasco building under fire condition. The LS-DYNA program is used to investigate the cause of steel beam-to-column connection failure. Results of the nonlinear analysis of detailed numerical model confirms the failure modes of the structural elements such as columns, trusses, joists, beams, welds, and other structural elements investigated during the site visits. Design recommendations are provided based on the results from the fire analysis of the Plasco building.

The influence of the in-plane flexibility of floor systems on the seismic response of the structures may become significant, particularly when considerable floor slab cracking and yielding is expected. Since in recent years the composite floor systems (steel beams with upper concrete slab) have been used widely in the steel buildings, the investigation of the diaphragm behavior of composite floor systems subjected to lateral loads, is inevitable. As a part of a comprehensive study of the effective parameters in the diaphragm behavior and in-plane characteristics of the composite floor systems, two half-scale single story building models with the parameter of the direction of the joists were tested. The scale-model structures were steel buildings with composite floor system consisting of four square panels supported by side frames with X bracing. The structures were designed under the seismic load specified in the seismic code of Iran, but to ascertain the inelastic behavior of the diaphragm, the stiffness of the lateral load resisting system of the structures were increased by doubling the number of bracings, then the cyclic lateral load was applied to the structures up to failure. The paper reports on the results of the test program performed at the structural engineering laboratory of Building and Housing Research Center of Iran (BHRC). The results show that the composite diaphragms present good performance under lateral loads; however the diaphragms'' in-plane characteristics such as stiffness, ultimate strength, stiffness degradation and the crack pattern of the floor slabs are affected significantly by the relative direction of the floor joists to the lateral load (perpendicular or parallel).

Due to the large number of fire and the resulting financial and human costs, it is necessary to prevent the roof from collapsing as one of the key members of the building during a fire. Because concrete has an inherent weakness in tensile stress, cracking in the tensile area of slabs is inevitable. On the other hand, in a system of prestressed concrete joist slab system, the tensile area of the concrete is usually completely eliminated or effectively reduced, and the performance of the floor can be expected to improve under fire conditions. The critical temperature was obtained and compared in 9 samples that differed in the amount of prestressing force, strength and concrete cover as well as the span length. The thermal load was applied to the studied samples according to the ISO 834-1 standard protocol. The temperature distribution across the slab was applied uniformly and incrementally and the failure states in the model were predicted and verified with laboratory results. The results showed that the prestressing force has the greatest effect and the span length has the least effect on decreasing or increasing the critical temperature index. Changing the prestressing parameter from zero to 600 and 1120 MPa, increases the critical temperature index by 20 and 43% and changing the beam length parameter from the initial value of 4.5 m to 6 and 7.5 m, decreasing the critical temperature index by 1 and 2%, respectively. Changing the parameter of concrete cover from 20 mm to 10 and 30 mm has caused a decrease and increase of critical temperature index by 11 and 9%, respectively. Also, in all samples, the same failure mode occurred in the middle of the joist in a bending manner.