• Computers and Concrete
• /
• v.26 no.4
• /
• pp.317-325
• /
• 2020

A precise estimation of the natural time period of buildings improves design quality, causes a significant reduction of the buildings' weight, and eventually leads to a cost-effective design. In this study, in order to optimise the reinforced concrete frames design, some symmetrical and unsymmetrical buildings composed of solid and hollow members have been simulated using finite element software SAP 2000. In numerical models, different parameters such as overturning moment, story drift, deflection, base reactions, and stiffness of the buildings were investigated and the results have been compared with strength and serviceability limit criteria proposed by Australian Standard (AS 3600 2018). Comparing the results of the numerical modelling with existing standards and performing a cost analysis proved the merits of hollow box sections compared to solid sections. Finally, based on numerical simulation results, two equations for natural time period of moment resisting reinforced concrete buildings have been presented. Both derived equations reflected higher degree of correlation and reliability with different complexities of building when compared with existing standards and relationships provided by other scholars. Therefore, these equations will assist practicing engineers to predict elastic behaivour of structures more precisely.

• Steel and Composite Structures
• /
• v.22 no.5
• /
• pp.1055-1071
• /
• 2016

The paper presents an innovative steel moment frame with the replaceable reinforced concrete wall panel (SRW) structural system, in which the replaceable concrete wall can play a role to increase the overall lateral stiffness of the frame system. Two full scale specimens composed of the steel frames and the replaceable reinforced concrete wall panels were tested under the cyclic horizontal load. The failure mode, load-displacement response, deformability, and the energy dissipation capacity of SRW specimens were investigated. Test results show that the two-stage failure mode is characterized by the sequential failure process of the replaceable RC wall panel and the steel moment frame. It can be found that the replaceable RC wall panels damage at the lateral drift ratio greater than 0.5%. After the replacement of a new RC wall panel, the new specimen maintained the similar capacity of resisting lateral load as the previous one. The decrease of the bearing capacity was presented between the two stages because of the connection failure on the top of the replaceable RC wall panel. With the increase of the lateral drift, the percentage of the lateral force and the overturning moment resisted by the wall panel decreased for the reason of the reduction of its lateral stiffness. After the failure of the wall panel, the steel moment frame shared almost all the lateral force and the overturning moment.

• Steel and Composite Structures
• /
• v.49 no.1
• /
• pp.47-64
• /
• 2023

Due to their efficient use of materials, hybrid reinforced concrete-steel (RCS) systems provide more practical and economic advantages than traditional steel and concrete moment frames. This study evaluated the seismic design factors and response modification factor 'R' of RCS composite moment frames composed of reinforced concrete (RC) columns and steel (S) beams. The current International Building Code (IBC) and ASCE/SEI 7-05 classify RCS systems as special moment frames and provide an R factor of 8 for these systems. In this study, seismic design parameters were initially quantified for this structural system using an R factor of 8 based on the global methodology provided in FEMA P695. For analyses, multi-story (3, 5, 10, and 15) and multi-span (3 and 5) archetypes were used to conduct nonlinear static pushover analysis and incremental dynamic analysis (IDA) under near-field and far-field ground motions. The analyses were performed using the OpenSees software. The procedure was reiterated with a larger R factor of 9. Results of the performance evaluation of the investigated archetypes demonstrated that an R factor of 9 achieved the safety margin against collapse outlined by FEMA P695 and can be used for the design of RCS systems.

• Computers and Concrete
• /
• v.9 no.2
• /
• pp.133-151
• /
• 2012

This paper presents an analytical procedure for the analysis of high strength steel fiber reinforced concrete members considering the cracking effect in the serviceability loading range. Modifications to a previously proposed formula for the effective moment of inertia are presented. Shear deformation effect is also taken into account in the analysis, and the variation of shear stiffness in the cracked regions of members has been considered by reduced shear stiffness model. The effect of steel fibers on the behavior of reinforced concrete members have been investigated by the developed computer program based on the aforementioned procedure. The inclusion of steel fibers into high strength concrete beams and columns enhances the effective moment of inertia and consequently reduces the deflection reinforced concrete members. The contribution of the shear deformation to the total vertical deflection of the beams is found to be lower for beams with fibers than that of beams with no fibers. Verification of the proposed procedure has been confirmed from series of reinforced concrete beam and column tests available in the literature. The analytical procedure can provide an accurate and efficient prediction of deflections of high strength steel fiber reinforced concrete members due to cracking under service loads. This procedure also forms the basis for the three dimensional analysis of frames with steel fiber reinforced concrete members.

• Structural Engineering and Mechanics
• /
• v.63 no.5
• /
• pp.669-681
• /
• 2017

The design of reinforced concrete buildings must satisfy the serviceability stiffness criteria in terms of maximum lateral deflections and inter story drift in order to prevent both structural and non-structural damages. Consideration of plastic hinge formation is also important to obtain accurate failure mechanism and ultimate strength of reinforced concrete frames. In the present study, an iterative procedure has been developed for the analysis of reinforced concrete frames with cracked elements and consideration of plastic hinge formation. The ACI and probability-based effective stiffness models are used for the effective moment of inertia of cracked members. Shear deformation effect is also considered, and the variation of shear stiffness due to cracking is evaluated by reduced shear stiffness models available in the literature. The analytical procedure has been demonstrated through the application to three reinforced concrete frame examples available in the literature. It has been shown that the iterative analytical procedure can provide accurate and efficient predictions of deflections and ultimate strength of the frames studied under lateral and vertical loads. The proposed procedure is also efficient from the viewpoint of computational time and convergence rate. The developed technique was able to accurately predict the locations and sequential development of plastic hinges in frames. The results also show that shear deformation can contribute significantly to frame deflections.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.23 no.5
• /
• pp.509-516
• /
• 2010

In this study a seismic retrofit scheme for the reinforced concrete moment framed structures was investigated using steel bracing and moment frames. The analysis model structure is a 3-story 3-bay moment frame structure designed only for gravity load. The stress/strain concentration in brace-RC frame connection was investigated using finite element analysis. To prevent premature joint failure, steel moment frames were placed inside of middle bay of the RC frame. Two types of braces, steel braces and buckling restrained braces(BRBs), were used for retrofit, and the ductility and the strength of the structure before and after the retrofit were compared using nonlinear static and dynamic analyses. According to the analysis results, the strength and ductility of the structure retrofitted by the moment frames and braces increased significantly. The added steel frame did not contribute significantly to the increase of lateral strength mainly because the size is relatively small.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.303-308
• /
• 2000

The design of column joint is an important part of earthquake resistant design of reinforced concrete moment resisting frames. Beam column joints must provide sufficient stiffness and strength to resist and sustain the loads induced by adjacent beams and columns. This paper investigates the difference of the current design codes which provide a different approach for the design of beam column joint in seismic zone. The model provided by Hitoshi Shiohara(1998) is reviewed in this paper, which provides a good relationship between moment and shear action of interior beam column joint and a role shear reinforcement according to their position.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10a
• /
• pp.438-443
• /
• 1998

Softening os the name used for decreasing bending moment at advanced flexural deformation. To accommodate softening deformation in analysis, it is assumed that a hinge has finite length. The softening analysis of R/C frames relies on the primary assumption that softening occurs over a finite hinge length and that the moment-curvature relationship for any section may be closely described by a trilinear approximation. A stiffness matrix for elastic element with softening regions are derived and the stiffness matrix allows extension of the capability of an existing computer program for elastic-plastic analysis to the softening situation. The effect of softening on the collapse load of R/C frame is evaluated.

• Steel and Composite Structures
• /
• v.23 no.1
• /
• pp.115-130
• /
• 2017

A new type of moment-resisting bolted connection was developed for use in composite steel- concrete construction to connect composite open section steel beams to concrete filled steel square tubular columns. The connection was made possible using anchored blind bolts along with two through bolts. It was designed to act compositely with the in-situ reinforced concrete slab to achieve an enhanced stiffness and strength. The developed connection was incorporated in the design of a medium rise (five storey) commercial building which was located in low to medium seismicity regions. The lateral load resisting system for the design building consisted of moment resisting frames in two directions. A major full scale test on a sub-assembly of a perimeter moment-resisting frame of the model building was conducted to study the system behaviour incorporating the proposed connection. The behaviour of the proposed connection and its interaction with the floor slab under cyclic loading representing the earthquake events with return periods of 500 years and 2500 years was investigated. The proposed connection was categorized as semi rigid for unbraced frames based on the classification method presented in Eurocode 3. Furthermore, the proposed connection, composite with the floor slab, successfully provided adequate lateral load resistance for the model building.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.688-691
• /
• 2004

This study summarizes results of a research project aimed at investigating the inelastic rotation capacity of beam-column joints of reinforced concrete moment frames. A total of 28 specimens were classified as special moment frame connections based on the design and detailing requirements in the ACI 318-99 provisions. Then, the acceptance criteria, originally defined for steel moment frame connections in the AISC-97 Seismic Provisions, were used to evaluate the joint connections of concrete moment frames. Twenty seven out of 28 test specimens that satisfy the design requirements for special moment frame structures provided sufficient strength and are ductile up to a plastic rotation of $3\%$ without any major degradation in strength.