Simplified slab design approach for parking garages with equivalent vehicle load factors

Kwak, Hyo-Gyoung,Song, Jong-Young Techno-Press 2000 Structural Engineering and Mechanics, An Int'l Jou Vol.9 No.3

This paper develops a simplified, but effective, algorithm in obtaining critical slab design moments for parking garages. Maintaining the uniformly distributed load concept generally adopted in the design of building structures, this paper also introduces the equivalent vehicle load factors, which can simulate the vehicle load effects without taking additional sophisticated numerical analyses. After choosing a standard design vehicle of 2.4 tons through the investigation of small to medium vehicles made in Korea, finite element analyses for concentrated wheel loads were conducted by referring to the influence surfaces. Based on the obtained member forces, we determined the equivalent vehicle load factors for slabs, which represent the ratios for forces under vehicle loads to these under uniformly distributed loads. In addition, the relationships between the equivalent vehicle load factors and sectional dimensions were also established by regression, and then used to obtain the proper design moments by vehicle loads. The member forces calculated by the proposed method are compared with the results of four different approaches mentioned in current design codes, with the objective to establish the relative efficiencies of the proposed method.

Nonlinear dynamic analysis of RC frames using cyclic moment-curvature relation

Kwak, Hyo-Gyoung,Kim, Sun-Pil,Kim, Ji-Eun Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.3

Nonlinear dynamic analysis of a reinforced concrete (RC) frame under earthquake loading is performed in this paper on the basis of a hysteretic moment-curvature relation. Unlike previous analytical moment-curvature relations which take into account the flexural deformation only with the perfect-bond assumption, by introducing an equivalent flexural stiffness, the proposed relation considers the rigid-body-motion due to anchorage slip at the fixed end, which accounts for more than 50% of the total deformation. The advantage of the proposed relation, compared with both the layered section approach and the multi-component model, may be the ease of its application to a complex structure composed of many elements and on the reduction in calculation time and memory space. Describing the structural response more exactly becomes possible through the use of curved unloading and reloading branches inferred from the stress-strain relation of steel and consideration of the pinching effect caused by axial force. Finally, the applicability of the proposed model to the nonlinear dynamic analysis of RC structures is established through correlation studies between analytical and experimental results.

An improved pushover analysis procedure for multi-mode seismic performance evaluation of bridges : (1) Introduction to numerical model

Kwak, Hyo-Gyoung,Shin, Dong-Kyu Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.33 No.2

This paper introduces an improved modal pushover analysis (IMPA) which can effectively evaluate the seismic response of multi-span continuous bridge structures on the basis of modal pushover analysis (MPA). Differently from previous modal pushover analyses which cause the numerical unstability because of the occurrence of reversed relation between the pushover load and displacement, the proposed method eliminates this numerical instability and, in advance the coupling effects induced from the direct application of modal decomposition by introducing an identical stiffness ratio for each dynamic mode at the post-yielding stage together with an approximate elastic deformation. In addition to these two introductions, the use of an effective seismic load, calculated from the modal spatial force and applied as the distributed load, makes it possible to predict the dynamic responses of all bridge structures through a simpler analysis procedure than those in conventional modal pushover analyses. Finally, in order to establish validity and applicability of the proposed method, correlation studies between a rigorous nonlinear time history analysis and the proposed method were conducted for multi-span continuous bridges.

Thermal-pressure loading effect on containment structure

Kwak, Hyo-Gyoung,Kwon, Yangsu Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.50 No.5

Because the elevated temperature degrades the mechanical properties of materials used in containments, the global behavior of containments subjected to the internal pressure under high temperature is remarkably different from that subjected to the internal pressure only. This paper concentrates on the nonlinear finite element analyses of the nuclear power plant containment structures, and the importance for the consideration of the elevated temperature effect has been emphasized because severe accident usually accompanies internal high pressure together with a high temperature increase. In addition to the consideration of nonlinear effects in the containment structure such as the tension stiffening and bond-slip effects, the change in material properties under elevated temperature is also taken into account. This paper, accordingly, focuses on the three-dimensional nonlinear analyses with thermal effects. Upon the comparison of experiment data with numerical results for the SNL 1/4 PCCV tested by internal pressure only, three-dimensional analyses for the same structure have been performed by considering internal pressure and temperature loadings designed for two kinds of severe accidents of Saturated Station Condition (SSC) and Station Black-out Scenario (SBO). Through the difference in the structural behavior of containment structures according to the addition of temperature loading, the importance of elevated temperature effect on the ultimate resisting capacity of PCCV has been emphasized.

Tension stiffening effect of RC panels\r\nsubject to biaxial stresses

Hyo-Gyoung Kwak,Do-Yeon Kim 한국계산역학회 2004 Computers and Concrete, An International Journal Vol.1 No.4

An analytical model which can simulate the post-cracking nonlinear behavior of reinforced concrete (RC) members such as bars and panels subject to uniaxial and biaxial stresses is presented. The proposed model includes the description of biaxial failure criteria and the average stress-strain relation of reinforcing steel. Based on strain distribution functions of steel and concrete after cracking, a criterion to consider the tension-stiffening effect is proposed using the concept of average stresses and strains. The validity of the introduced model is established by comparing the analytical predictions for reinforced concrete uniaxial tension members with results from experimental studies. In advance, correlation studies between analytical results and experimental data are also extended to RC panels subject to biaxial tensile stresses to verify tAn analytical model which can simulate the post-cracking nonlinear behavior of reinforced concrete (RC) members such as bars and panels subject to uniaxial and biaxial stresses is presented. The proposed model includes the description of biaxial failure criteria and the average stress-strain relation of reinforcing steel. Based on strain distribution functions of steel and concrete after cracking, a criterion to consider the tension-stiffening effect is proposed using the concept of average stresses and strains. The validity of the introduced model is established by comparing the analytical predictions for reinforced concrete uniaxial tension members with results from experimental studies. In advance, correlation studies between analytical results and experimental data are also extended to RC panels subject to biaxial tensile stresses to verify the efficiency of the proposed model and to identify the significance of various effects on the response of biaxially loaded reinforced concrete panels. he efficiency of the proposed model and to identify the significance of various effects on the response of biaxially loaded reinforced concrete panels.

Numerical models for prestressing tendons in containment structures

Kwak, Hyo-Gyoung,Kim, Jae Hong Elsevier 2006 Nuclear engineering and design Vol.236 No.10

<P><B>Abstract</B></P><P>Two modified stress–strain relations for bonded and unbonded internal tendons are proposed. The proposed relations can simulate the post-cracking behavior and tension stiffening effect in prestressed concrete containment structures. In the case of the bonded tendon, tensile forces between adjacent cracks are transmitted from a bonded tendon to concrete by bond forces. Therefore, the constitutive law of a bonded tendon stiffened by grout needs to be determined from the bond–slip relationship. On the other hand, a stress increase beyond the effective prestress in an unbonded tendon is not section-dependent but member-dependent. It means that the tendon stress unequivocally represents a uniform distribution along the length when the friction loss is excluded. Thus, using a strain reduction factor, the modified stress–strain curve of an unbonded tendon is derived by successive iterations. In advance, the prediction of cracking behavior and ultimate resisting capacity of prestressed concrete containment structures using the introduced numerical models are succeeded, and the need for the consideration of many influencing factors such as the tension stiffening effect, plastic hinge length and modification of stress–strain relation of tendon is emphasized. Finally, the developed numerical models are applied to prestressed concrete containment structures to verify the efficiency and applicability in simulating the structural behavior with bonded and/or unbonded tendons.</P>

방호구조물의 설계 및 해석

곽효경(Hyo-Gyoung Kwak),홍정욱(Jung-Wuk Hong) 한국콘크리트학회 2019 콘크리트학회지 Vol.31 No.5

인장강화 효과를 고려한 초고강도 강섬유보강 철근콘크리트 보 부재 수치해석

곽효경(Kwak, Hyo-Gyoung),나채국(Na, Chaekuk) 한국콘크리트학회 2009 한국콘크리트학회 학술대회 논문집 Vol.2009 No.5

쌍계1교 재하시험에 대한 극한한계상태 해석

곽효경 ( Kwak Hyo-gyoung ),김재홍 ( Kim Jae Hong ),나채국 ( Na Chaekuk ) 한국구조물진단유지관리공학회 2008 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.12 No.1

Assessment of an existing structure is a big issue to confirm the structural safety since infrastructures get deteriorated and damaged. Infrastructure assessment research center (ISARC) has tried to develop and apply new techniques for safety evaluation of concrete infrastructures. In accordance with the efforts, this paper shows an analytical evaluation of load-carrying capacity of a bridge. The target is a reinforced concrete T-girder bridge named as Ssanggye-1. The measured geometry of members and estimated properties of material are the input for ultimate limit state analysis. The analysis assumes the scenario of crisis with the proof load testing accomplished beforehand. Comparison between the analytical prediction and the experimental results shows good agreement and systematizes the analytical evaluation of load-carrying capacity.

부분 강합성보의 슬립거동

곽효경(Kwak Hyo Gyoung),서영재(Seo Young Jae) 대한토목학회 2000 대한토목학회논문집 A Vol.20 No.6A