• Steel and Composite Structures
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• v.31 no.6
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• pp.559-573
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• 2019

Spiral spacing effect on axial compressive behavior of reinforced concrete filled steel tube (RCFST) stub column is experimentally investigated in this paper. A total of twenty specimens including sixteen square RCFST columns and four benchmarked conventional square concrete filled steel tube (CFST) columns are fabricated and tested. Test variables include spiral spacing (spiral ratio) and concrete strength. The failure modes, load versus displacement curves, compressive rigidity, axial compressive strength, and ductility of the specimens are obtained and analyzed. Especially, the effect of spiral spacing on axial compressive strength and ductility is investigated and discussed in detail. Test results show that heavily arranged spirals considerably increase the ultimate compressive strength but lightly arranged spirals have no obvious effect on the ultimate strength. In practical design, the effect of spirals on RCFST column strength should be considered only when spirals are heavily arranged. Spiral spacing has a considerable effect on increasing the post-peak ductility of RCFST columns. Decreasing of the spiral spacing considerably increases the post-peak ductility of the RCFSTs. When the concrete strength increases, ultimate strength increases but the ductility decreases, due to the brittleness of the higher strength concrete. Arranging spirals, even with a rather small amount of spirals, is an economical and easy solution for improving the ductility of RCFST columns with high-strength concrete. Ultimate compressive strengths of the columns are calculated according to the codes EC4 (2004), GB 50936 (2014), AIJ (2008), and ACI 318 (2014). The ultimate strength of RCFST stub columns can be most precisely evaluated using standard GB 50936 (2014) considering the effect of spiral confinement on core concrete.

• Korean Journal of Animal Reproduction
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• v.15 no.1
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• pp.49-57
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• 1991

This study was carried out to investigate the effect of equilibration time, precooling and straw loading method on the post-thaw survival rates of mouse embryos cryopreserved by vitrification method. The effect of the vitrification procedure on the damage of the embryos was also examined by the straining of nuclei using Hoechst 33342. The results obtained were summarized as follows; 1. The equilibration in Medium-1 for 10 minutes was considered to be the optimum equilibration time. Embryos equilibrated in Medium-1 for 10 minutes(81.0%) showed significantly(P<0.05) higher survival rates than those equilibrated for 5 minutes(40.0%) or 15 minutes(74.1%). 2. The survival rate of embryos cryopreserved using the double Medium-2 column(81.0%) was significantly(P<0.01) higher than that using the single Medium-2 column, whish was considered to be due to the double Medium-2 column method being more reliable for preventing contamination of diluent solution of 1M sucrose. 3. The survival rate of compacted morula stage embryos cryopreserved with the precooled and non-precooled Medium-2 was not significantly(P<0.05) different. 4. The number of blastomeres of embryos at late blastocyst stage after culture of mouse morulae for 24 to 28hours was significantly(P<0.05) decreased by freezing embryos using vitrification(53.3${\pm}$1.6 vs 41.4${\pm}$1.5), which was considered to be due to the damage of embryos during vitrification and the delay of embryo development by handling in vitro. 5. The vitrification procedure is considered to be a very simple and efficient method for cryopreservation of embryos at early developmental stage.

• Earthquakes and Structures
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• v.11 no.2
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• pp.217-243
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• 2016

The linear and nonlinear seismic responses of steel buildings with perimeter moment resisting frames and welded connections (WC) are estimated and compared with those of buildings with post-tensioned connections (PC). Two-dimensional (2D) and three-dimensional (3D) structural representations of the buildings as well as global and local response parameters are considered. The seismic responses and structural damage of steel buildings with PC may be significantly smaller than those of the buildings with typical WC. The reasons for this are that the PC buildings dissipate more hysteretic energy and attract smaller inertia forces. The response reduction is larger for global than for local response parameters. The reduction may significantly vary from one structural representation to another. One of the main reasons for this is that the energy dissipation characteristics are quite different for the 2D and 3D models. In addition, in the case of the 3D models, the contribution of each horizontal component to the axial load on an specific column may be in phase each other during some intervals of time, but for some others they may be out of phase. It is not possible to observe this effect on the 2D structural formulation. The implication of this is that 3D structural representation should be used while estimating the effect of the PC on the structural response. Thus, steel frames with post-tensioned bolted connections are a viable option in high seismicity areas due to the fact that brittle failure is prevented and also because of their reduced response and self-centering capacity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.4
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• pp.17-26
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• 1991

Numerical methods are developed to obtain the critical loads and to analyze the post-buckling behaviour of the linearly varying tapered columns. The non-dimensional differential equations governing the elastica of post buckled column are derived by third order and solved numerically using the Runge-Kutta method and Regula-Falsi method. Three kinds of cross-sectional shape with simply supported end constraint are applied in unmerical examples. As the numerical results, the equlibrium paths. the typical elastica of post buckled columns and the critical load vs. section ratio curves are presented in figures. Also, the effects of cross-sectional shape factor on critical loads and postbuckling behaviour are presented in tables.

• Steel and Composite Structures
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• v.5 no.4
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• pp.271-287
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• 2005

The seismic behavior of two steel moment-resisting frames, which satisfy all the current seismic design requirements, are evaluated and compared in the presence of pre-Northridge connections denoted as BWWF and an improved post-Northridge connections denoted as BWWF-AD. Pre-Northridge connections are modeled first as fully restrained (FR) type. Then they are considered to be partially restrained (PR) to model their behavior more realistically. The improved post-Northridge connections are modeled as PR type, as proposed by the authors. A sophisticated nonlinear time-domain finite element program developed by the authors is used for the response evaluation of the frames in terms of the overall rotation of the connections and the maximum drift. The frames are excited by ten recorded earthquake time histories. These time histories are then scaled up to produce some relevant response characteristics. The behaviors of the frames are studied comprehensively with the help of 120 analyses. Following important observations are made. The frames produced essentially similar rotation and drift for the connections modeled as FR type and PR type represented by BWWF-AD indicating that the presence of slots in the web of beams in BWWF-AD is not detrimental to the overall response behavior. When the lateral displacements of the frames are significantly large, the responses are improved if BWWF-AD type connections are used in the frames. This study analytically confirms many desirable features of BWWF-AD connections. PR frames have longer periods of vibration in comparison to FR frames and may attract lower inertia forces. However, calculated periods of the frames of this study using FEMA 350 empirical equation is longer than those calculated using dynamic characteristics of the frames. This may result in even lower design forces and may adversely influence the design.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.7-15
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• 2008

Currently existing high-accuracy and high-speed die sets used in reciprocal press create scratches at the surface of guide posts, steel balls, and bushes due to vertical movement of balls with point-contacts between inner surface of bushes and guide posts. Consequently, accuracy of the die set and the life span of the metal mold are reduced. However, those scratches could reduce the pre-load of the steel ball. This research designed and developed a groove-type die set which improves life span of the die set by eliminating point-contacts of steel balls with guide posts. The guide post consisted of a steel-ball retainer, a steel-ball retainer stopper, a guide bush, a guide pin, a snap ring, and a spring. The steel-ball retainer has 72 holes with 8 columns of 9 holes in each column. The inner surface of the guide bush was grinded(surface roughness: $Ra\;\\;0.2{\mu}m$, accuracy: $0\;{\sim}\;-0.002mm$) after NC turning and heat treatment. Also, a line of small intermediate pocket was processed inside of the guide bush for lubrication and elimination of foreign materials. Guide grooves of steel balls were processed using a wire EDM(Electrical Discharge Machining) after heat treatment. With such a design of the guide post stated above, loads against steel balls could be dispersed greatly by the line contacts through the guide groove between the guide post and the guide bush, and the life span of the guide post could be expanded semi-permanently.

• Journal of the Korean Wood Science and Technology
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• v.39 no.1
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• pp.8-14
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• 2011

Japanese larch glulam was used as structural members to develop a modern engineered wood jointing system using traditional post and beam structure. For the connections comprised of traditional joining and drift-pins, structural members are processed at a pre-cut factory. As a basic study to examine and increase the whole shear performance of portal frame, pin withdrawal test and moment resistance tests were conducted on each connection. The post and beam members with specified connectors showed good bearing performance in the wood members' joining system, column-base and beam-end. Moment rigidity was a bit better in a joint with higher slenderness ratio of drift-pin, but moment resistance performances, yield moment and maximum moment, were excellent in smaller one.

• Computers and Concrete
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• v.20 no.6
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• pp.663-670
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• 2017

The post-tensioned (PT) flat plate slab system is commonly used in practice, and this simple and fast construction method is also considered to be a very efficient method because it can provide excellent deflection and crack control performance under a service load condition and consequently can be advantageous when applying to long-span structures. However, a detailed design guideline for evaluating the lateral behavior of the PT flat plate slab system is not available in current design codes. Thus, typical design methods used for conventional reinforced concrete (RC) flat plate slab structures have inevitably been adopted in practice for the lateral load design of PT flat plate structures. In the authors' previous studies, the unified equivalent frame method (UEFM) was proposed, which considers the combined effect of gravity and lateral loads for the lateral behavior analysis of RC flat plate slab structures. The aim of this study is to extend the concept of the UEFM to the lateral analysis of PT flat plate slab structures. In addition, the stiffness reduction factors of torsional members on interior and exterior equivalent frames were newly introduced considering the effect of post-tensioning. Test results of various PT flat plate slab-column connection specimens were collected from literature, and compared to the analysis results estimated by the extended UEFM.

• Steel and Composite Structures
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• v.38 no.1
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• pp.17-31
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• 2021

Post-earthquake fire is a common disaster which causes serious safety issues to infrastructures. This study aims to investigate the residual loading capacities of circular concrete-filled steel tube (CFST) columns under post-earthquake fire experimentally and numerically. The experimental programme contains two loading steps - pre-damage cyclic loading at room temperature and transient state tests with constant compression loads. Three finite element models are developed and validated against the test results. Upon validation, a total of 48 numerical results were generated in the parametric study to investigate the effects of thickness and strengths of steel tube, axial compression ratio and damage degree on the fire resistance of circular CFST columns. Based on the analysis on experimental and numerical results, the loading mechanism of circular CFST columns is discussed. A design method is proposed for the prediction of fire resistance time under different seismic pre-damage and compression loads. The predictions by the new method is compared with the newly generated experimental and numerical results and is found to be accurate and consistent with the mean value close to the unity and a coefficient of variation around 1%.

• Structural Engineering and Mechanics
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• v.73 no.3
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• pp.303-317
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• 2020

In this study an innovative rocking zipper braced frame (RZBF) is proposed to overcome the deficiencies of common concentrically braced frames. RZBF is an improved rocking concentrically braced frame which is based on combination of rocking behavior and zipper columns. The base rocking joints and post-tensioned bars provide rocking response and restoring force, respectively. Also, zipper columns distribute the unbalance force over the frame height and reduce the damage concentration. To evaluate seismic performance of RZBF, a comparison study is carried out considering concentrically braced frame, zipper braced frame, rocking concentrically braced frame and RZBF. Thereby, a suite of non-linear time history analyses had been performed on four different types of archetypes with four, six, eight, ten and twelve stories. Frames were designed and non-linear time history analyses were conducted in OpenSees. To compare the seismic behavior of the archetypes, roof drifts, residual roof drifts, story drifts, the forces of first and top story braces, PT bars forces, column uplift and base shears were taken in to consideration. Results illustrate that using RZBF, can reduce the damage due to reduced residual drifts. Zipper columns enhance the seismic performance of rocking systems. As the number of stories increase in the RZBF systems, larger top story braces were needed. So the RZBF system is applicable on low and midrise buildings.