Joint Details Research Articles

Buckling Strength of Single Angle Struts Part 3: Cross-Bracing in Tower Structure

Single angle cross bracings are customarily used in tower structures. According to the joint detailing, there exists not only force eccentricity but also rotational restraint at member ends. In addition, interaction occurs at the member buckling within a bracing panel, as well as within the two portions of a member. All these render the stability calculation rather complicate. In the current codes for tower design, simplified formulae of equivalent slenderness are given so as the member stability can be calculated as axially compressed struts. But these formulae are somewhat crude, giving unbalanced reliability. In this study, basing on the theory of elastic stability, and considering member buckling interaction in close coordination with joint detailing, formulae with better accuracy and reliability are put forward. One of the features of the proposed approach is the distinction between the cross-bracings connected to single angle leg post and those connected to a doubly symmetric leg post. The second feature lies in the refined formulae for specific interaction cases. The suggested formulae correlate well with available test data. Moreover, examination of test results reveals that it is unnecessary to specify lower buckling strength for cross-bracing bars connected by one bolt, provided that there is no in-plane eccentricity at the joint.

Buckling Strength of Single Angle Struts Part 2: Angles Connected by One Leg at Both Ends

A single angle strut connected at both ends by one leg is simple in execution, but complex in behavior. As a monosymmetric section, the angle is subjected simultaneously to compression, biaxial bending and torsion. Furthermore, there exist at the two ends rotational restraints whose rigidity depends on the member arrangement and joint detailing of the truss. So, a rigorous solution of the bearing capacity of such angle is very difficult to establish. The common practice in design work is to transform this complex problem into the buckling of an axially compressed strut, hinged at both ends, by taking an equivalent slenderness ratio. In this study, new formulas for this equivalent slenderness are suggested, where a concept of partial adjustment is introduced so that they apply to angles of high strength steel as well as to those of low carbon steel. The detrimental effect of torsion on the strut capacity is not negligible when the angle has slender leg, especially for high strength steel. Formulas of reduction factor to the member yield strength are proposed in this regard and are given as a function of the flat width-thickness ratio instead of the overall width-thickness ratio of the leg. These formulas, in conjunction with those for equivalent slenderness, correlate well with the test program of angle struts, steel grade 460 MPa. Lastly, limitations to the formulas of equivalent slenderness are discussed.

Detailing of I-beam-to-CHS column joints with external diaphragm plates for seismic actions

In this paper monotonic and cyclic finite element (FE) analyses are presented for the development of an I-beam-to-CHS column steel moment joint for seismic actions. The development process for the final joint details includes: (1) eliminating two identified structural deficiencies of distortion in column web panel and strain concentrations in the external diaphragms; (2) creating a multi-fuse energy dissipation mechanism; (3) devising a joint to delay onset of beam yielding. Two external diaphragm collar plates are welded to the circumference of the CHS column for connection to beam flanges. Various collar ring widths are examined for these horizontal diaphragms and a width (based on achieving full strength of the beam flanges) is found to produce an acceptable web panel performance. Different types of stiffener geometries in the connection region are then trialed to eliminate strain concentrations in the diaphragms. Two pairs of triangular diaphragm stiffeners are found to provide the desired performance. In order to produce a multi-fuse energy dissipation mechanism, tapered cover plates (TCPs) equipped with vertical stiffeners (VSs) are integrated into the joint. Oversized web holes of 4–10mm are required to enable inelastic deformation for an overall joint rotation of 60–100mrad, without undesirable web distortion. Further FE analyses are used to design the TCPs and VSs so they can be replaceable link post-seismic actions. For the final joint detailing it is shown that 6mm oversized holes for the TCPs will delay the occurrence of yielding in the beam until the joint rotation is 70mrad.

Experimental behaviour of friction T‐stub beam‐to‐column joints under cyclic loads

AbstractEurocode 8 has introduced the possibility of adopting partial‐strength joints for seismic‐resistant MR frames, provided it is demonstrated that connections perform adequately under cyclic loads. A programme of experiments devoted to investigating the cyclic behaviour of traditional joint details has recently been carried out by the authors. Within this programme, the analysis of the results obtained has revealed that even though connections designed to dissipate the seismic energy in bolted components can provide significant advantages because they are easy to repair after a destructive seismic event, they possess reduced dissipation capacity when compared with RBS connections and traditional full‐strength joints. An advanced approach aimed at enhancing the hysteretic behaviour of double split tee (DST) joints and the ambitious goal of preventing joint damage is presented here. The system proposed is based on the idea of using friction dampers within the components of beam‐to‐column joints. A preliminary set of prototypes has been tested experimentally and the performances of joints under cyclic loading conditions have been compared with those of traditional joint details. The experimental work was carried out at the Materials

Seismic performance study on exterior beam-column joint with mechanical anchorage for different joint core details

In the present study, in reinforced concrete structures, beam-column connections are one of the most critical regions in higher seismic prone areas. Proper reinforcement anchorage is essential to enhance the performance of the joints. Congestion of reinforcement and construction difficulties are reported frequently while using the conventional reinforcement detailing in the joint core area. An attempt has been made to study and evaluate the performance of joints with anchorage detailing as per American Concrete Institute (ACI)-352, ACI-318, and Indian Standard (IS)-456 along with confinement as per IS-13920 and without confinement. Apart from a solution for these problems, significant improvements in seismic performance, ductility, and strength were observed while using the mechanical anchorage (headed bar) in combination with X-cross plus hair clip (U-bar) joint reinforcement for higher seismic prone areas. To evaluate the performances of these types of anchorages and joint details, the specimens were assembled into two groups, each group having three specimens were tested under reversal loading and the same are presented in this paper.

Bayesian Probabilistic Framework for Damage Identification of Steel Truss Bridges under Joint Uncertainties

The vibration-based structural health monitoring has been traditionally implemented through the deterministic approach that relies on a single model to identify model parameters that represent damages. When such approach is applied for truss bridges, truss joints are usually modeled as either simple hinges or rigid connections. The former could lead to model uncertainties due to the discrepancy between physical configurations and their mathematical models, while the latter could induce model parameter uncertainties due to difficulty in obtaining accurate model parameters of complex joint details. This paper is to present a new perspective for addressing uncertainties associated with truss joint configurations in damage identification based on Bayesian probabilistic model updating and model class selection. A new sampling method of the transitional Markov chain Monte Carlo is incorporated with the structure’s finite element model for implementing the approach to damage identification of truss structures. This method can not only draw samples which approximate the updated probability distributions of uncertain model parameters but also provide model evidence that quantify probabilities of uncertain model classes. The proposed probabilistic framework and its applicability for addressing joint uncertainties are illustrated and examined with an application example. Future research directions in this field are discussed.

Tensile Testing of Groove Welded Joints Joining Thick-HSA800 Plates

In this study, a standard tensile welded-joint test was conducted to select a welding electrode suitable for recently developed HSA800 steel. Two welding electrodes were available at the time of this study; one was GMAW-based and the other FCAW-based. The tensile test specimens were fabricated by joining 60mm-thick HSA800 plates according to the AWS-prequalified groove welded joint details. Specimens which violate the standard root opening distance (ROD) were also included to see if poor construction tolerance could be accommodated. During fabrication, serious concerns about the welding efficiency of the GMAW-based product were raised by a certified welder. Both welding electrodes showed satisfactory and similar performance from welded joint strength perspective. But groove welded joints made by using the FCAW-based rod consistently showed more ductile and stable behavior. The AISC provisions for PJP joint strength were shown to be very conservative under direct tensile loading. Violating the AWS prequalified ROD by 100% apparently passed the strength criteria, but unusual crater-like fracture surface was observed.

Laplacian coordinates-based motion transition for data-driven motion synthesis

As a fundamental technique in data-driven (or example-based) methods, motion blending has been employed to produce new motion clip from two or more clips or introduced as a medium to improve the final result of other method, for example, motion graphs. As methods of motion blending always require the system or users to classify the motion samples, it is difficult to accomplish motion blending automatically and to preserve local details, such as angular accelerations of joints of original motions. In this study, the authors developed a framework based on Laplacian coordinates to produce transitions between two motion clips, emphasising on preserving local details, without any need of motion classification. At first, multidimensional Laplacian coordinates are introduced to present local details of joints' angle. Then an error function is deduced to measure how much result motions differ from original ones in local details. By minimising such error function, new motions can then finally generated, which can preserve local details of input motion clips as much as possible. The following experiments show the effectiveness of the authors' framework.

강재교각 기초부의 연결상세 개선을 위한 실험적 연구

현재 강재교각 기초부의 설계에 적용되어지고 있는 형식은 기초 콘크리트 내부에 앵커프레임을 설치하여 교각부와 연결하는 형태로 설계 및 시공을 하고 있다. 이는 복잡한 설계와 시공으로 인하여 기초부의 크기가 커지고, 과대 설계되는 경향이 있다. 본 연구에서는 고성능강을 이용한 교각 기초부의 연결상세와 관련하여 새로운 형상을 제안하기 위하여 기존 설계기준에 의한 시험체와 고장력 앵커를 사용한 새로운 연결형상 시험체 등 총 3개의 시험체를 제작하여 실내 시험을 실시하였다. 이를 통하여 각 시험체의 성능을 비교 분석하여 연결형식에 따른 구조물의 거동특성을 분석하였다. Generally, a steel pier-foundation has been designed and constructed with a anchor frame. However, because of the complicated design and construction, the foundation's size has become large and has been overdesigned. In this study, three specimens were made and the tests were conducted to suggest a new shape in regard to the pier-foundation's joint details using the high performance steel. One of the specimens was made up of the general anchors and the anchor frame. Another specimen consisted of the high tension anchors and the studs, and the other specimen was composed of the high tension anchors and the inner steels. After the performance of each specimen was compared and analyzed, the behavior characteristics according to the joint were analyzed.

Principles of a component-based connection element for the analysis of steel frames in fire

In this paper an approach is developed for practical modelling of the in-plane behaviour of connections between steel structural elements in global 3-dimensional frame analysis when structures are subject to heating by accidental fires. Because of the interactions between high deflections, thermal expansion and material weakening at high temperatures, connections are subject to considerable variation of both normal forces and moments in fire, so that it is insufficient to represent their behaviour simply in the moment–rotation terms which are usually adequate at ambient temperature. In order to analyse this behaviour reliably, use of the component-based approach is the only feasible method (short of creating highly complex finite element models) which can be included in non-linear, full-frame or subframe, numerical modelling. In previous work non-linear “spring” formulations have been developed and validated for the principal components which occur in the most commonly used steel-to-steel joint details, particularly for endplate connections, taking into account the local geometry, temperature and loading history. The principles governing the creation of connection elements, presenting just two nodes to the connected structural members, from assemblies of such components, are described for connections subject predominantly to two-dimensional structural actions.

Optimum Joint Detail for a General Cold-Formed Steel Portal Frame

In cold-formed steel portal framing systems that use bolted moment connections, formed through brackets, for the eaves and apex joints, it is well-known that the joints are semi-rigid, have finite connection-lengths and limited moment capacity. For such frames, it is therefore necessary for these joint effects to be taken into account when conducting frame design and analysis. However, as the semi-rigidity and the finite connection-lengths of each joint influence the bending moment distribution as well as the deflected profile of the frame, the joint detail for the eaves and the apex should not be designed independently of the frame. In this paper, a method of determining the optimum joint detail is described. It is demonstrated that careful selection of the joint detail can result in as much as a 25% increase in efficiency of the frame. Including joint effects explicitly into the design process provides better opportunities to devise the most appropriate balance between joints and member properties and thus reduce material use and construction costs.

Behaviour of fibre reinforced beam-column sub-assemblages under reversed cyclic loading

The potential of usage of steel fibre reinforced concrete (FRC) in structural components like beam-column joints under cyclic loading has been explored in the present study. Three different types of beam-column sub-assemblages, i.e. (i) with normal concrete, and designed according to Indian Standard and Eurocode including seismic joint detailing (Type A), (ii) adopting modified reinforcement detailing but including FRC and, (iii) designed for target joint failure (Type B) as well as flexural failure (Type C), have been considered. The specimens were experimentally investigated under repetitive reversed cyclic loading. Performance of the specimens under cyclic loading is evaluated in terms of failure mode, energy dissipation, strength degradation, shear deformation, strain development in reinforcement, etc. It has been found that longitudinal reinforcements of FRC specimen were found to be yielded at the face of the column and joint failure was completely avoided. At a drift level of ±5%, both the code based ductile specimens (Type A) showed a strength deterioration of 30% after the third cycle whereas Type B and Type C specimens experienced 10% and 20%, respectively. The present study has also brought out that all specimens of Type B performed better than Eurocode based reference ductile (Type A) in terms of energy dissipation. It is also observed that flexural specimens (Type C) were able to dissipate higher seismic energy than that obtained from Indian Standard based full ductile specimen (Type A). The results and observations of the present study would help in understanding the behaviour of critical regions of structures such as beam-column sub-assemblages and the efficacy of usage of FRC in those joints under cyclic loading.

Research and Application of Pre-Stressed Concrete Composite Slabs

The pre-stressed concrete composite slab, which combines the advantages of cast-in-place slabs and precast slabs, has promising development prospects. In the paper, according to structural integrity, bond performance, sound insulation, thermal preservation and construction techniques, four categories composite slab, such as the composite slab with flat bottom panel (including the composite slab with bar truss reinforced precast concrete bottom panel), the concrete composite slab with precast ribbed panel, the composite slab with hollow bottom panel and the composite slab with sandwich bottom panel are studied. The composite slab with flat bottom panel has poor structural integrity, and its bond performance and crack resistance of edge joint details need to be improved; the composite slab with bar truss reinforced precast concrete bottom panel has enough bond force, but its storage and transportation are inconvenient; the concrete composite slab with precast ribbed panel has good structural integrity and convenient construction procedure; the composite slab with hollow bottom panel and the composite slab with sandwich bottom panel have functions of sound insulation and thermal preservation, however they are inadequacy to resist bending moment and have complex construction procedure. The concrete composite slab with precast ribbed panel is provided with good mechanical behavior, economy and practicability, and is worth further researching and promoting.

Methods of improving the survival temperature in fire of steel beam connected to CFT column using reverse channel connection

This paper presents the results of a numerical study, using ABAQUS, of the behaviour and methods of improving the survival temperatures in fire of steel beams to concrete filled tubular (CFT) columns using reverse channel connection. The beams are axially restrained by the connected columns and develop catenary action so their survival temperatures are primarily controlled by the joint tensile resistance and deformation capacity. Therefore, improving the beam survival temperature mainly relies on improving the joint performance. This study investigates five different joint types of reverse channel connection: extended endplate, flush endplate, flexible endplate, hybrid flush/flexible endplate and hybrid extended/flexible endplate. The connection details investigated include reverse channel web thickness, bolt diameter and grade, using fire-resistant (FR) steel for different joint components (reverse channel, end plate and bolts) and joint temperature control. The effects of changing the applied beam and column loads are also considered. It is concluded that by adopting some of the joint details to improve the joint tensile strength and deformation capacity, it is possible for the beams to develop substantial catenary action to survive very high temperatures. However, it is important that the additional catenary force in the beam is resisted by the connected columns.

U형 강봉을 사용한 PC 계단 접합부 개발

프리캐스트 콘크리트는 현장작업을 최소화하고 공사품질을 보장할 수 있으며 공사기간을 단축시킬 수 있는 장점을 갖고 있다. 특히 계단실의 경우 재래식 거푸집을 사용할 경우 골조공사의 품질저하와 다수의 인력투입에 따른 생산성의 저하 및 시공의 어려움 등의 문제점이 있다. 본 연구에서는 PC 계단 접합부 상세를 개발하고, 제안한 접합부의 일체성확보와 사용성 및 안전성을 검증하기 위해 구조성능실험을 수행하였으며, 단순 핀접합 실험체에 비해 구속도의 증가, 내력, 강성 및 연성의 증가를 확인할 수 있었다. Compared with the traditional RC system, precast stairs can save construction time, reduce the cost of concrete casting, etc. This paper focuses on an investigation of improved continuous longitudinal joint details for PC stair systems. The performance of the precast concrete stair connections subjected to displacement control cyclic loading is compared with that of the monolithic connection. The developed connection is composed of U-rods and clamp joint metals. This paper proposes precast stair connection with improved structural performance and experimentally evaluates the structural performance of the proposed joints in terms of maximum load, displacement ductiliy, strain, crack and failure modes.

Transverse Joint Details with Tight Bend Diameter U-Bars for Accelerated Bridge Construction

AbstractThis paper focuses on an investigation of transverse joint details with tight bend diameter U-bars for accelerated bridge construction. It presents the testing results of potential alternate reinforcing materials and joint details in two phases. Headed bar and U-bar [stainless steel and deformed wire reinforcement (DWR)] specimens with the same joint detail configuration were tested and compared in Phase I, followed by testing of U-bars (DWR) with varied concrete strength, bar spacing, and overlap length in Phase II. Test results were evaluated based on tension capacity, cracking at service loading and failure, and steel strain. A strut-and-tie model is proposed to predict the tension capacity of a transverse joint, which is capable of identifying the most critical parameters and yields safe and consistent predictions. Based on the experimental results, a No. 5 U-bar joint detail with no less than 152 mm (6 in.) overlap length and No. 4 lacer bars was recommended.

Structural details of steel girder–abutment joints in integral bridges: An experimental study

Integral bridges, which have integrated superstructures and substructures, should essentially maintain the rigid behavior and structural safety of the various existing joints. Especially temperature sensitive, girder-abutment joints for integral steel bridges are steel–concrete composite structures and require sufficient rigid behavior. Yet, various design guidelines and standards do not state these specific designs or construction methods. This study proposes structural details of girder-abutment joints in integral steel bridges for enhanced rigid behavior and load-resisting and crack-resisting capacity. Thus, this study additionally suggests various joints that apply stud shear connectors and perfobond rib shear connectors to existing empirically constructed girder-abutment joints. This study verifies the performance and evaluates the behavior of the proposed steel girder-abutment joints through experimental loading tests of empirically constructed joint specimens and specimens of the proposed joints. Also, this study performs FE analysis (non-linear structural analysis), which applies contact interaction of the interface of the steel–concrete composite joints. As a result of the experimental loading test, all the existing empirical joints and the proposed joints demonstrated sufficient rigidity and crack-resisting capacity under required design and yield load and are applicable as girder-abutment joints for integral steel bridges. Moreover, the proposed joints are judged to be structurally superior to the empirically constructed joints by the results of analysis for load-displacement relationships, crack-propagation behaviors, and load-strain relationships. Like the proposed girder-abutment joints in this study, joints with improved rigid behavior and load-resisting and crack-resisting capacity may resolve and properly control durability and serviceability issues of integral bridges.

Investigation of closure-strip details for connecting prefabricated deck systems

This article describes how the Bridge Office of the Ministry of Transportation of Ontario initiated a research project to investigate the use of precast bridge technology as an innovative approach to bridge construction and rehabilitation in 2001. Two potential precast systems were investigated: precast composite slab-on-girder beam elements connected with cast-in-place concrete closure strips, and full-depth precast concrete deck slab panels laid across new or existing girders and connected with cast-in-place concrete closure segments. One of the main issues inherent in these precast systems is the presence of cold joints created by the closure pours and their potential effect on the overall deck system behavior. In addition, there is a need to develop effective connection details between the precast elements to provide continuity of reinforcement in the closure strips so that load sharing between girders is not compromised. This article presents the findings of a series of laboratory tests that were performed on 2/3-scale model of the closure strip system to study the serviceability and ultimate state behavior of the joint detail. Several types of reinforcement lapping systems were considered for the steel reinforcement in the closure strips: U-shaped bars, L-shaped bars, welded straight bars, and straight bars with full lap splice length as well as splices with reduced lap length but confined by steel spirals or stirrups. Scale models of the closure-strip connections were subjected to extensive cyclic loading and then tested to failure. Overall, the test results demonstrated the excellent performance of U-shaped, L-shaped, and welded straight reinforcing bars as connection details in the closure strips. The use of high-early-strength concrete in the closure pour was shown to have little effect on long-term performance, while a shortened lap length confined in a steel spiral was shown to be as effective as the conventional full-lap-length splice detail.

Study of Fatigue Tests on the Structural Details of Welding Joints of Integral Bridge Deck and Main Girder Gusset Plates

Under the action of both dead and live loads, the welding joints of the integral bridge deck and the main truss gusset plates of a steel truss bridge in the transverse and longitudinal directions are all subjected to tensile force, the fatigue performance of which greatly influence the safety and durability of the bridge during operation. Fatigue tests were carried out on a full-scale model designed and made in accordance with the structural details of the welding joints of the integral bridge deck and the main truss gusset plates of Dashengguan Changjiang River Bridge. On the basis of the results of the fatigue tests, the stress distribution of the welding joints was analyzed, the fatigue life of the welding joints under load cycles with constant amplitude was discussed and the fatigue performance of the welding joints under the condition of two-way tensile forces was studied. It is concluded that under the effect of fatigue loading with given amplitude, the fatigue life of the welding joints is more than 200 million numbers of load cycles, the structural details of welding joints have ample fatigue resistant ability under the condition of two-way tensile forces, and the maximum main stress value of the fatigue tests is lower than the allowable fatigue stress value given in various codes and relevant references and the fatigue strength meets requirement.

Parametric Study and Length Limitations for Prestressed Concrete Girder Integral Abutment Bridges

This study establishes a practical limit for the maximum length of prestressed concrete girder integral abutment bridges (IABs) and identifies potential distress in IABs at extreme lengths. The nonlinear numerical models developed using detailed three-dimensional solid elements include soil-pile interaction, abutment-pile interaction, and construction joint detail. The loads on IABs were ambient temperature, temperature gradient, time-dependent loads, and backfill pressure. A parametric study was performed with an initial bridge length of 305 m considering the effects of: (a) abutment height; (b) soil stiffness; (c) backwall to abutment stiffness; and (d) pile orientation on IAB response. Results of the parametric study showed that taller abutments, moderate construction joint stiffness, low soil stiffness, and strong axis pile orientation are best suited for IABs at extreme lengths. The length limitation study identifies that pile moments and concrete stress at the abutment/pile connection, concrete stress and transverse threading reinforcement shear stress at girder/backwall connection, and construction joint reinforcement are critical components in IAB responses and limit the bridge length. Finally, this study suggested a maximum length of 457 m on the basis of IAB critical responses.