To solve the shortcomings of single-limb or double-limb cold-formed thin-walled steel column easy to buckling failure and low bearing capacity, a new cross-shaped built-up cold-formed thin-walled steel multi-limb-section is proposed for columns. The structure is composed of several single-limb cold-formed thin-walled steel C-channel sections. The flanges and webs are connected by self-drilling screws. In order to assess the mechanical properties of this built-up multi-limb-section column and the influence of the slenderness ratio on the column behavior, the axial loading tests were carried out. Three kinds of single-limb column and built-up multi-limb-section column with different ratio of slenderness were tested. The deformation process, failure mode and bearing capacity were analyzed. The SC specimens failed with local buckling and distorted buckling, while the MC and LC specimens failed with local buckling and global instability. For the built-up multi-limb-section column, the section combination multiple is 12. Compared to the section combination multiple, the bearing capacity combination multiple is much higher. The SQ specimens' combination factor is about 1.1, the combination factor of MQ specimens and LQ specimens are about 1.4 and 3.0, respectively. It is concluded that the overall combined-performance and structural efficiency of the specimens is proportional to the combination factor.

This paper presents a research on optimum design of cold-formed steel space frames using a new algorithm method named Jaya, which has been developed in recent years. The most obvious difference of Jaya algorithm from other algorithms is that it does not need any control parameters for updating. However, Jaya algorithm is able to successfully reach the optimum solutions without any delay. In this study, in order to test the robustness and practicality of this novel algorithm technique, different steel space frame problems that have been studied with other algorithms in literature are examined. The minimum weight designs of the problems are carried out by selecting suitable C-section from a prepared list including 85 C-sections with lips taken from American Iron and Steel Institute (AISI 2008). A program is coded in MATLAB interacting with SAP2000 OAPI (Open Application Programming Interface) in order to obtain optimum solutions. The strength constraints according to AISI-LRFD (Load and Resistance Factor Design), lateral displacement constraints, inter-story drift constraints and geometrical constraints are taken into account in the analyses. Two different cold-formed steel space frames are taken from literature to research optimum solutions by using Jaya algorithm. The first steel space frame is 379-member and the second steel space frame is 1211-member. The results obtained using Jaya algorithm are compared with those in reference studies. The results prove that Jaya algorithm technique is quite successful and practical optimum design of cold-formed steel space frames.

The pleasing appearances, economic and easy construction of cable-stayed footbridges (CSFB) have made them one of the most preferred options for pedestrian traffic crossing over the highways. The basic structural members of CSFB can be sortable as a foundation, pylon, deck, and stay-cables. The stay-cable has an important role in the formation of structural integrity by ensuring that the deck and pylon work together with the help of proper post-tensioning forces (PTF) applied to them. In this study, it is aim to determine proper set of PTF with the help of the developed optimization process which provides to work together metaheuristic algorithm named Teaching-Learning-Based Optimization (TLBO) and Open Applicable Programming Interface (OAPI) properties of SAP2000 with codes created in MATLAB. In addition of this aim, the study also presents the importance of PTF for structural behavior of CSFB. TLBO algorithms use a randomly created initial population. The teacher phase and student phase are the main part of this algorithm. Five different proper sets of PTF are determined by using developed optimization process and the structural response such as displacement and internal forces of structural members of the selected CSFB compared with each other. Consequently, PTF directly affects the behavior of CSFB, as it ensures that displacements of deck and pylon remain between the acceptable limits, controls the distribution and magnitude of the internal forces for different load combinations. Furthermore, the evaluation of PTF might not have a single solution because CSFB are highly statically indeterminate so there are more different possible sets of PTFs that satisfy strength and serviceability requirements.

In this research, a new minimization-based controlled method was proposed to analyze steel plane truss structures undergoing large deformations. Non-linear solution was acquired by minimizing a constrained optimization problem via the genetic algorithm. The suggested procedure can directly predict buckling load and its corresponding displacements, and precisely trace equilibrium path of geometrically non-linear plane truss structures. A computer program was formed to anticipate both elastic pre- and post-buckling behaviors or any arbitrary point on equilibrium path of the structures subjected to abnormal loads. Notably, a load-deflection curve with multiple limit points and a complex snap-back phenomenon can be followed using the proposed method. Five truss examples were analyzed, and the acquired results were compared with those obtained by theoretical solution, modified arc-length, Newton-Raphson methods, and those reported in the literature to validate robustness and accuracy of the proposed procedure.

This investigation aims to examine the vibration phenomenon in 2D transversely isotropic homogeneous Euler-Bernoulli nonlocal nanobeam with laser pulse with new modified three-phase lag Green Naghdi (TPL GN) model. The model contains a material length scale parameter that can capture the size effect, using the nonlocal theory of thermoelasticity. Temperature is assumed to vary sinusoidally. Laplace Transforms are used to derive the non-dimensional expressions for lateral deflection, axial displacement, temperature distribution, axial stress, and thermal moment in the transformed domain, and numerical inversion techniques are used to find the expressions in the physical domain. The ends of the nanobeam are considered to be simply supported and have a constant temperature. Effect of new modified TPL GN heat transfer and nonlocal parameter is represented graphically for lateral deflection, axial displacement, temperature distribution, axial stress, and thermal moment using the MATLAB software. Few specific cases are also derived.

This paper presents the compressive behaviors of RPC-filled double skin steel tubular (RFDST) stub columns. Six RFDST stub column specimens, with different hollow ratios and constraint coefficients, were tested under axial compression loading. The compressive behaviors, such as failure mode, strength and ductility, were analyzed. It is found that the failure mode of RPC filled steel tube (RFST) stub column is shear failure, while RFDST stub columns are waist drum failure. The load deformation curves of RFDST specimens with different hollow ratio and constraint coefficient show different characteristics. RFDST specimens exhibit high bearing capacity and good ductility. Based on the test results of existing RFDST stub columns, a design formula for predicting the ultimate bearing capacity is given. A finite element model is also presented to analyze the compressive behaviors, and good agreement is obtained. The influences of hollow ratio and constraint coefficient on the ultimate bearing capacity are discussed.

Steel- concrete composite beams are widely used in the construction of tall building with steel floors. In these floors, the bearing capacity of beams in which the performance of concrete and steel is composite is more than 30% of the same beams with non-composite performance. Fire, especially in buildings, has a devastating effect on the components of the structure including the columns, beams, floors, etc. Also, fire indirectly affects the shear connectors buried in floor concrete and reduces their strength, thus reducing the overall strength of the floor. In this research, the behavior of angle shear connectors as a type of shear connectors used in the steel-concrete composite floor due to temperature increase was investigated numerically. Thermo-mechanical finite element modeling was performed using Abaqus software on push-out samples, and the results have been compared with the results obtained from the laboratory tests. Similar to the laboratory conditions, samples with different dimensions of angle shear connectors were modeled at different temperatures including 25, 550, 700 and 850 degrees Celsius. According to the laboratory process, 24 samples were modeled in Abaqus software thermally. The research results showed that the models made in the software were able to accurately predict the laboratory results including shear strength and slip. It was found that the maximum shear force error between analytical and laboratory results is 21.6% and the minimum shear force error in some samples is near to zero. As the temperature increases, the error rate between the laboratory and analytical results increases. Also, shear connector dimensions, concrete strength and temperature value have direct effect on the final strength of steel-concrete composite floors and load slip diagrams. It was also concluded that increasing the angle height to a certain extent could increase the final shear strength of the steel-concrete floor and increasing the angle height after a certain limit had no effect on increasing the shear strength and results in material loss and uneconomical design. Moreover, results indicated that increasing the temperature up to 850℃ leads to reducing the shear strength of the samples by approximately 56%.

To perform a nonlinear analysis of building frames in their seismic performance evaluation program, appropriate force-deformation curves of the structural members in linear and nonlinear phases which represent their actual behavior are required. Although these curves have been provided for common existing RC elements prior to retrofitting in available instructions, the codes are silent about appropriate practical models for strengthened elements. In this regard, a comprehensive numerical study is conducted in the Finite Element (FE) software VecTor2 to investigate the effects of various influential parameters on the moment-rotation behavior of CFRP-confined rectangular RC columns. The investigated parameters are cross-sectional dimensions, longitudinal and transverse reinforcement ratios, the level of column axial load, concrete compressive strength, and the effective confinement provided by external CFRP wraps. Then, through the idealization of the obtained moment-rotation curves, the influence of the aforementioned parameters on the plastic rotation capacity of the columns as one of the main required parameters to define the nonlinear behavior of the retrofitted columns is investigated. Accordingly, column axial load intensity, shear force, effective confinement, and column depth are found to be the major effective parameters on the plastic rotation capacity of the columns. Finally, a practical method consistent with ASCE 41-13 is presented to estimate the plastic rotation capacity of CFRP-confined columns.

The paper considers a 2D problem associated with a porous magneto-thermoelastic material under the effect of gravity in the context of the Three-Phase-Lag (3PHL) model and a 'memory dependent derivative frame. It has been assumed that during the initial stages, the medium is in an inactive state for the half-space (thermoelastic) the surface of this half-space is subjected to mechanical force and has a constant heat flux. The paper presents graphical illustrations of the variables under consideration as they vary along with the vertical distance. A number of figures are used to draw out several comparisons for the thermophysical quantities as they greatly assist in studying the effects of the gravity field, mechanical force, time, and thermal memories (relaxation times).

By using differential quadrature method (DQM), forced vibrational behavior of a porous functionally graded (FG) cylindrical scale-dependent shell in thermal environment and under a moving point load having constant velocity has been researched. Within the micro-size shell, porosities exist with even or uneven distributions. Accordingly, the material properties of the micro-size shell rely on porosities and may be defined utilizing refined power-law functions. Strain gradients have been incorporated because of the existence of size effects at micro scale. Established governing equations based on first-order shell theory have been arranged in Laplace form. Next, time responses of the micro-size shell have been calculated accomplishing inverse Laplace transform technique together with differential quadrature method (DQM). It may be understood that forced vibrational behaviors of micro-size shells are dependent on the load speed, strain gradient factor, pore volume, material gradation and temperature variation.