Beams In Moment Resisting Frames Research Articles

Numerical study on the rotation capacity of SIP-strengthened cold-formed steel beams

The use of cold-formed steel (CFS) beams in moment-resisting frames (MRFs) has recently become a topic of interest to many researchers. In this research, a numerical study has been performed to investigate an innovative seismic protection system and new energy dissipation technique called steel interconnected part (SIP), to allow CFS to be used in regions with high seismic activity. Through this technique, a steel part has been connected to 2C-channel back-to-back CFS beams to improve both strength and structural behavior. The steel part does not require much space because of its shape, which can be easily connected to the CFS beams. Finite element procedure in ABAQUS has been used to model the 2C-channel back-to-back connected with a through plate by bolts. In this paper, a total of 240 models have been studied under monotonic loading and 27 models under cyclic loading. The rotation capacity of CFS beams strengthened with SIP has been reported with different through plate dimensions. Different beam profile slenderness ratios with different geometric configurations for SIP have been studied. In the CFS beams without SIP, early loss of strength has been observed with premature flange and web buckling. The results revealed that the beams are strengthened using SIP can delay local failures and improve strength, initial stiffness, ductility and energy dissipation behavior, which cannot be attained by conventional CFS elements and connections. The proposed SIP system revealed promising results, that could achieve all the desired performance objectives and satisfy the requirements of common seismic codes.

Experimental-numerical study on weakened HSS-to-HSS connections using HBS and RBS approaches

Hollow structural sections (HSS) have been used more often as columns because of their symmetrical geometry and admissible performance in bearing axial forces along with bending and torsional moments. The use of hollow sections as beams in moment-resisting frames would be beneficial and is worthy to assess. To this aim and considering the importance of developing plastic bending hinges of the special moment-resisting frames in a zone far from the column face, two methods for weakening beam sections are studied and compared in this paper: 1) Reduced beam section (RBS) and 2) Heat-treated beam section (HBS). For the experimental investigation, a furnace was first made to heat the desired zone of the beam. Then, a cyclic quasi-static loading protocol was applied to two full-scale beam-column connection specimens. The experimental specimens were made by box sections in which the beams had reduced or heat-treated sections. Moreover, for verification and parametric studies, finite element models were generated using ABAQUS. The columns of numerical models had box sections whereas rectangular and circular hollow structural sections were used as beams. Additionally, the seismic behavior of two beam-column connection models with box and pipe heat-treated beam sections was investigated under near-field loading protocol. Compared with RBS sections, both the results of experimental and numerical studies indicated the acceptable bending behavior of heat-treated hollow structural sections in terms of prevention of lateral-torsional buckling along with a stable hysteretic behavior.

Shear Design of High Strength Concrete Beams in MRFs

This paper presents the criteria for the shear design of high strength concrete (HSC) beams in moment resisting frames (MRFs). The formulation of an analytical model is provided for the case of beams with longitudinal reinforcement in the presence of transverse stirrups. The model is of additive type, in the meaning that the shear resistance of the beam is evaluated as the sum of several contributions. In particular, the contribution of concrete, longitudinal rebars and transversal reinforcement are taken into account. Furthermore, for assessing the concrete contribution, a classical approach is followed, according to which two effects arise in the shear mechanism: the arc and the beam effect. The features of these two resisting mechanisms are particularized to the case of HSC in steel reinforced beams and the maximum concrete contribution is limited to the maximum compressive strength of the concrete strut in biaxial state of stress. Moreover, for the evaluation of the resistance contribution of the longitudinal steel rebars in tension, the model takes into account the residual bond adherence between HSC and steel reinforcement and the spacing between subsequent cracks. The results are compared with the prescriptions currently provided in the main building codes and with different analytical models existing in the literature. For the comparison, the analytical expressions are applied to a set of experimental data available in the literature and design observations are made on the geometrical percentage of steel bars, the resistance of materials, the residual bond stress and the depth-to-shear span ratio.