Tensile Strength and Concrete Cone failure in CFT Connection with Internal Diaphragms

김선희,최성모 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.2

Concrete filled tube (CFT) system provides excellent structural performance thanks to the composite effect between the tube and the concrete. However, its closed sections impose complication on the fabrication of the column-to-beam connection and only a small number of connection methods have been developed. In square CFT column-to-beam connections, internal diaphragms reinforce the inside of the column for the loads and moments delivered from the beam. It is required to develop various connection types to secure structural capacity and concrete filling. In the process of making the square Hollow steel section (HSS), diaphragms are placed in channel members in advance and then the two channel members are welded longitudinally to produce a square HSS. It is superior to other connection types in terms of the degree of Complication in placing the internal diaphragms, economical efficiency and workability. In this study, strength formulas were suggested based on the yield line theory to evaluate the load capacity of the column-to-beam connections. For the connection of horizontal diaphragms, the strength of steel tube faces, internal diaphragms, and concrete cone failure were accumulated. For the connection of vertical perforated plates, the strength of steel tube faces, concrete cone failure, and perfobond were accumulated. Although there was a slight difference between the formula and test result, it can be used to estimate the strength of columnto- beam connections.

보-기둥 접합부 Rigidity에 따른 PC 골조건물의 응답저감계수 변화에 관한 연구

서수연 忠州大學校 2003 한국교통대학교 논문집 Vol.38 No.2

Current design codes(1997 UBC, 1997 NEHRP Provisions) for precast concrete frame structures require the use of strong connections, unless the strength of the connectors at the required ductilities are demonstrated to be adequate by both suitable experimental and analytical methods. Then the response modification factors(RMF) appropriate for precast concrete frame buildings are to be the same as those for monolithic concrete frame buildings. However, where plastic hinging occurs in a connection , the expected response of the precast concrete frame building will differ from that of the monolithic frame building and depend on the characteristics of the connection. For that condition, estimates of the appropriate RMF for the precast concrete frame buildings are required because the response of such buildings may differ from those for monolithic frame concrete buildings. This study evaluates the nonlinear response characteristics of precast concrete frame buildings where plastic hinging occurs in the precast connection. Designs were developed for buildings 5, 10, and 15 stories in height for moderate seismic risk region of the U.S. The response of the buildings were analyzed using DRAIN-2DX(1992) and following the Nonlinear Static Analysis procedure. The main variables of the analysis are the strength and stiffness of the connection. Also, for the analysis, the bi-linear response model developed and inserted into the DRAIN-2DX program by Shan Shi and D. Fouch(1997), are used. It was shown that the strength of the buildings as well as their displacement capacities decreased with decrease of either the strength or stiffness in the connections. Therefore such changes also require reductions in RMF values for the buildings. The decreasing ratio of RMF of precast concrete frame buildings in accordance with reduced stiffness and strength of connection is proposed.

Investigations of different steel layouts on the seismic behavior of transition steel-concrete composite connections

Qi, Liangjie,Xue, Jianyang,Zhai, Lei Techno-Press 2019 Advances in concrete construction Vol.8 No.3

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

A new precast wall connection subjected to monotonic loading

Ramin Vaghei,Farzad Hejazi,Hafez Taheri,Mohd Saleh Jaafar,Abang Abdullah Abang Ali 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.17 No.1

Final construction project cost is significantly determined by construction rate. The Industrialized Building System (IBS) was promoted to enhance the importance of prefabrication technology rather than conventional methods in construction. Ensuring the stability of a building constructed by using IBS is a challenging issue. Accordingly, the connections in a prefabricated building have a basic, natural, and essential role in providing the best continuity among the members of the building. Deficiencies of conventional precast connections were observed when precast buildings experience a large induced load, such as earthquakes and other disasters. Thus, researchers aim to determine the behavior of precast concrete structure with a specific type of connection. To clarify this problem, this study investigates the capacity behavior of precast concrete panel connections for industrial buildings with a new type of precast wall-to-wall connection (i.e., U-shaped steel channel connection). This capacity behavior is compared with the capacity behavior of precast concrete panel connections for industrial buildings that used a common approach (i.e., loop connection), which is subjected to monotonic loading as in-plane and out-of-plane loading by developing a finite element model. The principal stress distribution, deformation of concrete panels and welded wire mesh (BRC) reinforcements, plastic strain trend in the concrete panels and connections, and crack propagations are investigated for the aforementioned connection. Pushover analysis revealed that loop connections have significant defects in terms of strength for in-plane and out-of-plane loads at three translational degrees of freedom compared with the U-shaped steel channel connection.

소성힌지 영역의 접합부를 개선한 PC 구조벽체의 개발

강수민,오재근,김욱종,이도범,박홍근 한국지진공학회 2010 한국지진공학회논문집 Vol.14 No.2

PC(Precast Concrete) 구조시스템은 건식화 조립식 공법으로 구조물 건설에 있어 공기, 노동력 절감 등의 여러 장점을 가지고 있다. 하지만 구조벽체의 경우 이를 PC화하여 사용할 경우 접합부의 내진성능이 떨어지므로 PC 구조벽체를 사용하는 경우는 드물다고 할 수 있다. 본 연구에서는 이러한 점을 감안하여 접합부 성능을 개선하여 횡력저항요소로 사용가능한 2종류의 PC 구조벽체를 제안하였다. 제안된 PC 구조벽체는 RC 벽체 및 PC 벽체가 혼합된 복합 PC 벽체와 벽체하부 연결철근의 일부를 단면감소시키고 비부착상세를 적용한 PC 벽체로서 지진발생 시 충분한 강도와 변형능력을 확보할 수 있도록 하였다. 제안된 PC 구조벽체의 내진성능평가를 위하여 RC 벽체를 포함한 3가지 벽체에 대한 실험체를 제작하여 주기 횡하중 실험을 수행하였다. 실험결과, 제안된 PC 구조벽체는 강도, 강성, 변형능력 및 에너지 소산능력이 기존 PC 구조벽체보다 월등히 향상되어 우수한 내진성능을 확보할 수 있는 것으로 나타났다. The purpose of this study is to develop a precast concrete structural wall system that can assure reliable seismic performance. In previous studies, the connections of precast concrete structural walls have had some problems in their seismic performance. Therefore, this research proposes precast concrete structural walls which have an improved seismic performance. One is a hybrid precast concrete structural wall that is composed of a reinforced concrete component and a precast concrete component, and another is a precast concrete wall whose reinforcements have a partially reduced section and are partially unbonded from the surrounding concrete. To evaluate the seismic performance of the proposed precast concrete structural walls, the behavior of three specimens, including a reinforced concrete wall, were subjected to reversed cyclic combined flexure and shear. According to the test results, the proposed precast concrete structural walls have reliable seismic performance.

Numerical Investigation of I-Shaped Beam to Concrete Filled Tube Column Connection Without Continuity Plate

Shohreh Sohaei,Mehrzad Tahamouli Roudsari,Parham Memarzadeh 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.6

Circular columns are increasingly being used in today’s construction industry. Proper construction beam-circular column connections are an important problem in steel moment resisting frames with this type of connection. TahamouliRoudsari et al. introduced a new I-shaped beam-circular concrete-fi lled column connection in 2020. This connection makes use of a strengthened U-shaped profi le as an external stiff ener with simple detailing. Experimental tests showed that the connection satisfi es code-specifi ed criteria for rigid connections. The main objective of the present work is to present design guidelines and a more accurate numerical investigation of the detailing introduced by TahamouliRoudsari et al. For this, in the fi rst step, a numerical model of the experimental specimen was constructed and verifi ed in the ABAQUS fi nite element software. Then, through multiple nonlinear fi nite element analyses, it has been demonstrated that this type of connection can meet all the requirements of special moment resisting frames with rigid connections. The minimum thickness for the strengthened U-shaped profi le has been determined in such a way so that the plastic hinge could be created in the beam and the connection would have suffi cient stiff ness to be categorized as fully restrained. The eff ects of the geometry of the stiff ened channel link and the column-to-beam section modulus ratio on the behavior of the connection were investigated and a relationship has been developed to calculate the thickness of the stiff ened channel profi le. Also, evaluating the eff ects of axial loading in the column showed that the thickness of the U-shaped profi le and the stiff eners have no bearing on the axial load applied to the column.

Influential factors on the level of spalling in fire exposed concrete

한동엽 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.6

The aim of this research is investigating the influential factors governing the level of concrete spalling at a material level. Fromthe former research on concrete spalling under the fire conditions, many available mechanisms have been provided andrecently, the spalling damage of concrete has been explained as a result of high inner pressure due to the evaporation of thewater in concrete microstructure. Based on the spalling mechanism, this study prepared various concrete specimens made withdifferent water-to-binder ratios, air contents, moisture contents, aggregate sizes, aggregate types and supplementarycementitious material (SCM) to investigate the governing factors on spalling of concrete. From the investigation, the factorswhich can cause pore connectivity, easiness of cracking, and moisture content of the concrete microstructure were governingfactors on spalling damage. Therefore, in this research, based on the results of the investigation it was possible to providecritical factors on spalling damage of the concrete, and it is expected that the data obtained from this study can provide usefulinformation for the design of fire resistant concrete.

Shear Tests on Subassemblies Representing the Multi-anchored Connection between PC Wall Panels and RC Frames

손국원,하수경,송근택,유승룡 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.12

When existing Reinforced Concrete (RC) framed structures are strengthened with Precast Concrete (PC) wall panels, a special connection is required that can accommodate the time-dependent deformation of the RC frame when using PC members made of the same size and resist a large shear force. In this study, we propose a connection that can solve both of these issues through overlapping anchors. The purpose of this study is to investigate and analyze the shear resistance of the overlapped anchor connections between the PC panel and the RC elements in modeling tests. A total of ten full-scale specimens of anchored connection models were constructed and push-out tested. Two anchor groups were installed in three concrete segments and overlapped in the connection of the specimens. The tested average shear strength of the overlapped anchored connections was 109% of the calculated values according to the American anchor design code. The results of this study show that the new anchored connection model can be analyzed using the American anchor design code. Therefore, we can predict the effect of the proposed connection, and it is expected that the design safety and construction practicability of the infill method will be improved using these connections.

Investigation of a new steel-concrete connection for composite bridges

Dimitrios Papastergiou,Jean-Paul Lebet 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.17 No.5

A new type of connection for steel-concrete composite bridges was developed by the Steel Structures Laboratory of Ecole Poytechinque Fédérale de Lausanne. Resistance to longitudinal shear is based on the development of shear stresses in the confined interfaces which form the connection. Confinement is provided by the reinforced concrete slab which encloses the connection and restrains the uplift (lateral separation) of the interfaces by developing normal stresses. The experimental investigation of the interfaces, under static and cyclic loading, enabled the development of the laws describing the structural behaviour of each interface. Those laws were presented by the authors in previous papers. The current paper focuses on the continuity of the research. It presents the experimental investigation on the new connection by means of push-out tests on specimens submitted to static and cyclic shear loading. Investigation revealed that the damage in the connection, due to cyclic loading, is expressed by the accumulation of a residual slip. A safe fatigue failure criterion is proposed for the connection which enabled the verification of the connection for the fatigue limit state with respect to the limit of fatigue. A numerical model is developed which takes into account the laws describing the interface behaviour and the analytical expressions for the confinement effect, the latter obtained by performing finite element analysis. This numerical model predicts the shear resistance of the connection and enables to assess its fatigue limit which is necessary for the fatigue design proposed.

An experimental study of the behaviour of double sided bolted billet connections in precast concrete frames

Halil Görgün 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.29 No.5

Precast concrete structures are erected from individual prefabricated components, which are assembled on-site using different types of connections. In the present design of these structures, beam-to-column connections are assumed pin jointed. Bolted billet beam to-column connections have been used in the precast concrete industry for many years. They have many advantages over other jointing methods in component production, quality control, transportation and assembly. However, there is currently limited information concerning their detailed structural behaviour under vertical loadings. The experimental work has involved the determination of moment-relative rotation relationships for semi-rigid precast concrete connections in full-scale connection tests. The study reported in this paper was undertaken to clarify the behaviour of such connections under symmetrical vertical loadings. A series of full-scale tests was performed on sample column for which the column geometry and bolt arrangements conformed to successful commercial practice. Proprietary hollow core floor slabs were tied to the beams by 2T25 tensile reinforcing bars, which also provide the in-plane continuity across the connections. The contribution of the floor strength and stiffness to the flexural capacity of the joint is currently neglected in the design process for precast concrete frames. The flexural strength of the connections in the double-sided tests was at least 0.93 times the predicted moment of resistance of the composite beam and slab. The secant stiffness of the connections ranged from 0.94 to 1.94 times the flexural stiffness of the attached beam. In general, the double-sided connections were found to be more suited to a semi-rigid design approach than the single sided ones. The behaviour of double sided bolted billet connection test results are presented in this paper. The behaviour of single sided bolted billet connection test results is the subject of another paper.