• Computers and Concrete
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• v.25 no.4
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• pp.327-341
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• 2020

Advanced forms of structural design (e.g., displacement-based methods) require knowledge of the non-linear force-displacement behavior of both the overall building and individual lateral load resisting elements, i.e., walls or building cores. Similarly, understanding the non-linear behaviour of the elements in a structure can also allow for a less conservative structural response to be calculated by better understanding the cracked (i.e., effective) properties of the various RC elements. Calculating the non-linear response of an RC section typically involves using 'black box' analysis packages, wherein the user may not be in complete control nor be aware of all the intricate settings and/or decisions behind the scenes. This paper introduces a user-friendly and transparent analysis program for predicting the back-bone force displacement behavior of slender (i.e., flexure controlled) RC walls, building cores or columns. The program has been validated and benchmarked theoretically against both commonly available and widely used analysis packages and experimentally against a database of 16 large-scale RC wall test specimens. The program, which is called WHAM, is written using Microsoft Excel spreadsheets to promote transparency and allow users to further develop or modify to suit individual requirements. The program is available free-of-charge and is intended to be used as an educational tool for structural designers, researchers or students.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.4
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• pp.191-199
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• 2016

Piloti-type building is one of typical vertical atypical buildings. These buildings can fail by weak-story or flexible-story mechanism on the first story. They should be designed by taking into account the special seismic load, but those less than six stories are not required to confirm the seismic performance from structural engineers in Korea. For this reason, small-size pilloti-type RC buildings need to be checked for seismic performance. Based on this background, this study performed nonlinear dynamic analysis using the PERFORM-3D for small-size pilloti-type RC buildings and assessed their seismic performance. Examples are two through four story buildings with and without walls in the first story. The walls and columns in the first story satisfied the target performance in the basic of flexural behavior due to quite a large size and reinforcement. However, wall shear demands exceed shear strength in some buildings. When designed for KBC2009, wall shear strength exceed shear demand in some buildings, but still does not in others. Consequently, wall shear must be carefully checked in both existing and new small-size pilloti-type RC buildings.

• Structural Engineering and Mechanics
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• v.44 no.2
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• pp.197-217
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• 2012

Detailed analysis of internal forces of exterior beam-column joints of RC frames under seismic action is reported in this paper. A formula is derived for calculating the average joint shear from the column shears, and a formula is proposed to estimate torque in eccentric joints induced by seismic action. Average joint shear stress and strain are defined consistently for exterior joints, which can be used to establish joint shear constitutive relationship. Numerical results of shear, bending moment and torque in joints induced by seismic action are presented for a pair of concentric and eccentric exterior connections extracted from a seismically designed RC frame, and two sections located at the levels of beam bottom and top reinforcement, respectively, are identified as the critical joint sections for evaluating seismic joint behavior. A simplified analysis of the effects of joint shear and torque on the flexural strengths of the critical joint sections is made for the two connections extracted from the frame, and the results indicate that joint shear and torque induced by a strong earthquake may lead to "joint-hinging" mechanism of seismically designed RC frames.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.195-202
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• 2002

Lap splices of longitudinal reinforcement steels were practically located in the potential plastic hinge region of most bridge columns that were constructed before the 1992 seismic design provision of Roadway Bridge Design Specification in Korea. The objective of this research is to evaluate the seismic performance of shear-critical reinforced concrete(RC) bridge piers with poor detailing of the starter bars in the plastic hinge region, and to develop the enhancement scheme of their seismic capacity by retrofitting with fiber composites. Seven test specimens in the aspect ratio of 2.5 were made with three confinement ratios and two types of lap splices. Quasi-static test was conducted in a displacement-controlled test mode. A significant reduction of displacement ductility ratios were observed for test columns with lap splices of longitudinal steels.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.324-330
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• 2005

The flexural strength and ductility capacity of reinforced concrete columns are largely dependent on the amount of transverse steel. However, current design code does not specify the confinement effect of transverse steels in strength calculation. A non-linear moment-curvature analysis of RC column sections was conducted in order to develop PM interaction diagram considering transverse reinforcement effects. In this paper, a more reasonable application method of PM interaction diagram considering transverse steel amounts is introduced and proposed, based on moment-curvature non-linear analysis. Also, we proposed simplified method to use. easily in practical design.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.475-482
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• 2002

A moment-curvature relationship to simulate the behavior of reinforced concrete (RC) columns under cyclic loading is introduced. Unlike previous moment4curvature models and the layered section approach, the proposed model takes into account the bond-slip effect by using a monotonic moment-curvature relationship constructed on the basis of the bond-slip relation and corresponding equilibrium equation at each nodal point. In addition, the use of curved unloading and reloading branches inferred from the stress-strain relation of steel gives more exact numerical result. The pinching effect caused by axial force is considered with an assumption that the absorbing energy corresponding to any deformation level maintains constant regardless of the magnitude of applied axial lone. The advantages of the proposed model, comparing to layered section approach, may be on the reduction in calculation time and memory space in case of its application to large structures. Finally, correlation studies between analytical result and experimental studies are conducted to establish the validity of the proposed model.

• Computers and Concrete
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• v.19 no.6
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• pp.689-699
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• 2017

An energy-based approach for determining earthquake safety of reinforced concrete frame structures is presented. The developed approach is based on comparison of plastic energy capacities of the structures with plastic energy demands obtained for selected earthquake records. Plastic energy capacities of the selected reinforced concrete frames are determined graphically by analyzing plastic hinge regions with the developed equations. Seven earthquake records are chosen to perform the nonlinear time history analyses. Earthquake plastic energy demands are determined from nonlinear time history analyses and hysteretic behavior of earthquakes is converted to monotonic behavior by using nonlinear moment-rotation relations of plastic hinges and plastic axial deformations in columns. Earthquake safety of selected reinforced concrete frames is assessed by using plastic energy capacity graphs and earthquake plastic energy demands. The plastic energy dissipation capacities of the frame structures are examined whether these capacities can withstand the plastic energy demands for selected earthquakes or not. The displacements correspond to the mean plastic energy demands are obtained quite close to the displacements determined by using the procedures given in different seismic design codes.

• Advances in concrete construction
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• v.6 no.2
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• pp.177-197
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• 2018

This paper presents a case study about the damages on the structural elements of a cast in place reinforced concrete (RC) building after a big fire which was able to be controlled after six hours. The fire broke off at the $2^{nd}$ basement floor of the building, which has five basements, one ground, and two normal floors. As a result of intensely stocked ignitable materials, it spread out to the all of the upstairs. In visual inspection, most of the typical fire damages were observed (such as spalling, net-like cracks, crumbled plasters, bared or visible reinforcement). Also, failures of the $2^{nd}$ basement columns were encountered. It has been concluded that the severity failures of the columns at the $2^{nd}$ basement caused utterly deformation of the building, which is responsible for the massive damages on the beam-column connections. All of the observed damages were categorized related to the types and presented separated regarding the floors. Besides to the visual inspection, the numerical analysis was run to verify the observed damaged on the building for columns, beams, and the connection regions. It is concluded from the study that several parameters such as duration of the fire, level of the temperature influence on the damages to the RC building. Also, it is highlighted by the study that if the damaged building is considered on the overall structural system, it is not able to satisfy the minimum service requirements neither gravity loads nor earthquake conditions.

• Computers and Concrete
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• v.27 no.5
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• pp.437-445
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• 2021

Retrofitting of structures has gained importance over the recent years. Particularly, Reinforced Cement Concrete (RCC) column strengthening has become a challenge to the structural engineers, owing to the risks and complexities involved in it. There are several methods of RCC column strengthening viz. RCC jacketing, steel jacketing and Fiber Reinforced Polymer (FRP) wrapping etc., FRP wrapping is the most promising alternative when compared to the others. The large research database shows FRP wrapping, through lateral confinement, improves the axial load carrying capacity of the columns under concentric loading. However, its confining efficiency reduces under eccentric loading. Hence a relative newer technique called Near Surface Mounting (NSM), in which Carbon FRP (CFRP) strips are epoxy grouted to the precut grooves in the cover concrete of the columns, has been thrust domain of research. NSM technique strengthens the column nominally under concentric load case while significantly under eccentric case. A novel configuration of NSM in which the vertical NSM (VNSM) strips are being connected by horizontal NSM (HNSM) strips was numerically investigated under both concentric and eccentric loading. It was found that the configuration with 6 HNSM strips performed better under eccentric loading than under concentric loading, while the configuration with 3 HNSM strips performed better under concentric loading than under eccentric loading. Hence an optimum of 4 HNSM strips is recommended as strengthening measure for the given column specifications. It was also found that Aluminum alloy cannot be used instead of CFRP in NSM applications owing to its lower mechanical properties.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.289-298
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• 2016

An experimental research was performed using fibers for the purpose of retrofitting existing reinforced concrete circular columns. Glass fiber (GF) and polyethylene terephthalate (PET) were used as well as combined GF+PET (HF). PET has high tensile strength (over 600 MPa) and high ductility (about 15%), but has very low elastic modulus (about 1/6 of GF). A total of four columns was tested against laterally applied reverse cyclic load: control column, GF-, PET-, and HF-strengthened columns. All columns retrofitted using fibers demonstrated improved moment capacity and ductility. Moment capacity of GF-, PET-, and HF-strengthened columns was 120%, 107%, and 120% of the control column, respectively. Drift ratio of all retrofitted columns also increased by 63 ~ 83% over the control column. The final failure mode of the control column was main bar buckling. The final failure mode of the GF- and HF-strengthened columns was GF rupture while that of the PET-strengthened column was main bar rupture in tension. No damage was observed for PET at the ultimate stage due to excellent strain capacity intrinsic to PET. Current test results indicate that PET can be effectively used for seismic retrofit of RC columns. It is noted that the durability characteristics of PET needs to be investigated in the future.