Sang-Whan Han

Stiffness Reduction Factor for Flat Slab Structures under Lateral Loads

Effective beam width model EBWM has been widely used for predicting lateral drifts and slab moments in flat slab structures under lateral loads. As the slab moment due to lateral loads increases, slab stiffness decreases due to crack formation. The accuracy of the EBWM strongly depends on how the reduced slab stiffness is estimated. For this purpose, this study developed equations for calculating slab stiffness reduction factor by conducting nonlinear regression analysis using stiffness reduction factors estimated from collected test results. The slab stiffness reduction factor is defined as a ratio of reduced slab stiffness due to crack formation to the stiffness of the uncracked slab section. For verifying the proposed equation, the lateral stiffness of two slab-column connection specimens tested by the writers was compared with the lateral stiffness calculated using the EBWM with the proposed stiffness reduction factor. Further, two flat plate specimens having two continuous spans were also considered for verifying the proposed equations for .

Cyclic Behavior of High-Performance Fiber-Reinforced Cement Composite Coupling Beam Having Diagonal Reinforcement

Coupled shear walls can provide an efficient structural system to resist lateral force. However, the reinforcement detail for diagonally reinforced coupling beams required by ACI-318 often causes the difficulties in construction due to the reinforcement congestion and interference among reinforcement. This paper is to evaluate cyclic behavior of High-Performance Fiber-Reinforced Cement Composite (HPFRCC) coupling beams having reduced transverse reinforcement around the beam perimeter. Experimental test was conducted using three specimens having a beam aspect ratio 2.0. Test results showed that HPFRCC coupling beams with half of transverse reinforcement required by ACI-318 provided similar energy dissipation capacities compared with the coupling beams having reinforcement satisfy the requirement of ACI-318.

Efficient Method for Selecting Ground Motions with a Mean Response Spectrum Matching a Target Spectrum

This paper proposes an efficient method for selecting ground motions with the mean response spectrum matching a target spectrum. Since former studies reported that the shape and amplitude of the response spectra can be treated independently for selecting ground motions, this study first selects ground motions such that the shape of their mean response spectrum matches that of the target spectrum, then scales the ground motions. To select the ground motions best matching the shape of the target response spectrum, the standard deviation of the difference between the target response spectrum and the mean response spectrum of the selected ground motions needs to be minimized. Unlike the existing procedure, the scaling factor can be computed without iteration. Based on the selection results of 7 ground motions from a library of 40 ground motions, the proposed method is verified as an accurate and efficient method.

Punching Shear Strength of the Void Transfer Plate

The transfer slab system is a structural system that transfers the loads from the upper shear wall structure to the lower columns. This is a costly system due to a very thick slab, and the relatively high cost can be mitigated by introducing voids in the slab. However, this system of flat plate containing voids is vulnerable to brittle failure caused by punching shear in vicinity of slab-column connection. Thus, the punching shear capacity of the void system is very important. However, the current code doesn`t provide a clear design provision for the strength of slabs with a void section. In this study, experimental study was conducted to investigate the punching shear strength of the void slab system. The shear strength of the specimens was predicted by current code and previous researches. In result, the punching shear strength of the void system is determined as the least value calculated at critical section located a distance d/2 from the face of the column and the center of the void section using the effective area at critical section.

Probability Based Determination of Slab Thickness Satisfying Floor Vibration Criteria

In current design practice, the thickness of the floor slab has been determined to satisfy requirement for deflection control. However, previous study shows that the floor thicknesses in residential buildings may not satisfy the floor vibration criteria, even though the thickness is determined by the serviceability requirements in current design provisons. Thus it is necessary to develop the procedure to determine slab thickness that satisfies the floor vibration criteria. This study attempts to propose slab thickness for flat plate slab systems that satisfies floor vibration criteria against occupant induced floor vibration(heel drop load). Two boundary conditions(simple and fixed support), three square flat plates(4, 6, 8m), and five concrete strength( MPa) are considered. Since there are large uncertainties in loading and material properties, probabilistic approach is adopted using Monte-Carlo simulation procedures.

Evaluation of Shear Strength of Precast-prestressed Hollow Core Slabs Based on Experiments

ABSTRACT The weight of concrete could be reduced by using hollow core slabs instead of heavy solid slabs, leading to cost reduction. The long span be also achieved by introducing prestress in hollow core slabs. but the evaluation of shear strength of precast-prestressed hollow core slabs are needed because the cross section is reduced in web and arranging shear reinforcement is not possible. In this study, the shear strength of precast-prestresse d hollow core slabs were evaluated based on experimental tests . For this purpose, six full scale specimens were made and tested. The shear strength of the specimens were compared with those evaluated from current design provision(EC2 ACI, EN1168 and AASHTO). Keywords : hollow-core slab, web-shear capacity, tensile strength of concrete, principal tensile stress, transfer length 1. 서 론 1) 프리캐스트 프리스트레스트 콘크리트(PC-PSC) 중 중공슬래브(Hollow Core Slab, 이하 HCS)는 슬래브 복부에 중공부를 만든 바닥구조시스템이다. 슬래브 복부의 중공부는 슬래브의 중량과 재료비용이 감소되는 장점이 있으나 복부단면의 감소로 전단에 취약하다. 또한 일반적으로 압출성형방식으로 제작되는 특성상 전단철근의 배근이 어려워서 전단에 취약하다. 이러한 이유 때문에 HCS 부재를 사용 시 복부전단에 대해 신중한 검토가 필요하다 .국내에서 HCS의 전단강도평가에 대한 연구는 미비한 상황이며, 기준에 대한 평가도 불분명한 상황이다. 현재 국내에서 HCS의 설계에 사용되는 KCI

Seismic Performance Evaluation of Steel Moment Resisting Frame Systems According to an Improved Design Method of RBS-B Connections

In current seismic design provisions, a reduced beam section with bolted web (RBS-B) connections is only permitted for intermediate moment frames (IMF). This study evaluated the seismic performance of steel moment resisting frame systems having RBS-B connections designed according to current seismic design provisions. For this purpose, 12 archetypal IMF systems having two different span lengths (9m, 6m) were designed considering two design load levels (SDC , SDC ). A nonlinear analytical model that can simulate hysteretic behavior of an RBS-B connection was also developed in this study. The procedures specified in ATC 63 are used to conduct a seismic performance evaluation. Moreover, this study conducts the seismic performance evaluation of IMF systems designed according to a new design method proposed by the authors in the previous study. It was observed that several model frames designed according to current seismic design provisions did not provide satisfactory collapse margin ratios (ACMR). This study also showed that the model frames designed according to the new design procedures had a sufficient ACMR.

Seismic Performance Evaluation of Steel Moment Resisting Frames with WUF‐B Connections

The purpose of this study is to evaluate the seismic performance of the moment resisting steel frames having Welded Unreinforced Flange‐Bolted web (WUF‐B) connections. The connections are designed and detailed in compliance with FEMA 350 recommended seismic design criteria. To conduct the seismic performance evaluation this study developed an analytical model for the pre‐ and post‐Northridge connections based on test results. Three different frames are considered which have three‐, nine‐ and twenty‐story. Incremental Dynamic Analysis (IDA is conducted to estimate limit state capacities The performance of the frames having either pre‐ or post‐Northridge connections is compared with the corresponding frame with ductile connections which do not experience connection fracture. The analytical results showed that buildings with post‐Northridge WUF‐B connections provide superior strength and interstory drift ratio capacity than buildings with pre‐Northridge WUF‐B connections.

Analytical Model for Post Tension Flat Plate Frames

This study developed an analytical model for predicting nonlinear behavior of PT flat plate frames having slab-column connections with and without slab bottom reinforcement passing through the column. The developed model can predict the failure sequence until punching failure occurs. For verifying the analytical model, the test results of PT flat plate slab-column connections were compared with the results of the analysis. Moreover, the results of static pushover test and shaking table test of 2 story PT flat plate frame were compared with analysis results. For evaluating seismic performance of PT flat plate frame, this study conducted nonlinear response history analysis of the 2 story PT flat plate frame with and without slab bottom reinforcement passing through the column under 1940 El Centro ground motion scaled to have pseudo spectral acceleration of 0.3, 0.5, and 0.7g at the fundamental period of the frame. This study observed that as ground motion is more intense, seismic demands for the frame having the connections without slab bottom reinforcement passing through the column are larger than those without slab bottom reinforcement.

Cyclic Behavior of Slender Reinforced Concrete Coupling Beams with Bundled Diagonal Reinforcement

Coupled shear walls are effective lateral force resisting system in which coupling beams link individual walls. For improving the energy dissipation capacity of coupling beams, diagonal reinforcement details were developed. However, it is difficult to construct diagonal reinforced coupling beams due to the congestion of reinforcement in the beam. For resolving the problem, this study developed precast coupling beams with bundled diagonal reinforcement. To reduce the reinforcement congestion, bundled diagonal reinforcement were placed in the coupling beam. To evaluate the cyclic performance of coupling beams with bundled diagonal reinforcement, experimental test were conducted. For this purpose, two slender specimens with an aspect ratio of 3.5 were made and tested. It was observed that the cyclic performance of the coupling beam with bundled diagonal reinforcement was similar with that of the coupling beam with normal diagonal reinforcement placed according to design code to ACI 318-11.