Beam End Connections Research Articles

A New Moment-Resisting Glulam Beam-End Connection Utilizing Mechanically Fastened Steel Rods—An Experimental Study

A new moment-resisting mass timber connection was designed based on the principles of force equilibrium in applied mechanics. The connection configuration utilizing two mechanically fastened threaded steel rods embedded into the end of a glulam beam section was experimentally investigated in this study. A gradually increasing transverse load was applied to the free end of a cantilevered beam, causing a bending moment on the beam-end connection until failure. Four different connection configurations were examined, each replicated twice to verify results. The beam connection parameters investigated were rod anchorage length (200 and 250 mm) and square washer size (38.1 and 50.8 mm). Test results show that increasing the washer size increased the connection bending strength by increments more significantly than those due to increasing the rod anchorage length. However, the connection configurations with the smaller-size washer, which failed mainly due to wood crushing under the washer, had higher ductility ratios than those with the larger-size washer, which failed due to steel rod yielding. In a real-life scenario, a structural element such as a glulam beam is usually loaded to approximately 50% to 70% of its design capacity, considering a reasonable margin of safety. The study estimates a maximum possible bending moment utilization factor for the strongest connection configuration that ranged between 34% and 48% compared to the maximum moment resistance of a supported glulam beam spanning an average length of 4.0 m to 6.0 m (a common span length in framed timber buildings) and has a cross-section size same as the one utilized in this study. This utilization factor is quite large for a timber connection, and thus, confirms a considerable moment-resisting capability of the new configuration developed in this study.

Effect of the Looseness of the Beam End Connection Used for the Pallet Racking Storage Systems, on the Mechanical Behavior of the Bearing Beams.

The worldwide use of pallet racking storage systems leads to the necessity for research regarding the effects of the clearance between the metallic tabs of the connector and upright slots (looseness effect) on the performance of load-bearing beams. Firstly, the looseness angle and the rotational stiffness were experimentally obtained for three types of beam-to-upright connections. A theoretical approach is used to investigate the magnitude of the looseness effects that occurred on the performances of the bearing beam of the pallet storage systems in terms of the bending moment developed at the midpoint of the beam and maximum deflection. Calculation corrections were evaluated for the connections involved in the experimental part, for the case which considers the looseness effects with respect to the case which does not consider the looseness effect. In order to evaluate the effects of the parameters of the connections on calculus corrections, the theoretical model was used for other types of beam-to-upright connections. It is shown that the maximum corrections are 2.99% and 5.16% for the bending moment developed at the midpoint of the beam and for the maximum deflection, respectively. It is proved that the connector type affects the size of the correction.

Fire resistance of a fully concealed, moment-resisting new timber connection utilizing mechanically-fastened steel rods

One major hindrance to more utilization of timber in the construction of tall buildings is the limited fire resistance of the connections between its structural elements. In an experimental study that aimed to investigate the structural behaviour of a new connection configuration that utilizes fully concealed, mechanically fastened steel rods, eight (8) full-size glued-laminated timber beam-end connections were tested under the CAN/ULC-S101 standard time-temperature curve. Test variables investigated in this study included rod anchorage length (200 and 250 mm) and washer size (38.1 × 38.1 and 50.8 × 50.8 mm). Results show that using the smaller washer provided more wood side cover to protect the steel components from the effects of elevated temperatures. Also, utilizing longer rod anchorage length provided larger internal surface area of the wood prism to better resist shear stresses as well as longer length for the rods to bear against the wood at high rotation values of the connection. By combining the said two aspects (longer anchorage length and smaller washer) a fully concealed glulam beam-end connection that utilizes only two mechanically-fastened steel rods can be successfully designed to achieve a 1-h fire resistance without the application of additional fire protection.

Fire performance of hybrid mass timber beam-end connections with perpendicular-to-wood grain reinforcement

PurposeThe fire resistance of timber structures is heavily dependent on the fire behaviour of the connections between its structural elements. The experimental study presented in this paper aimed to investigate the fire performance of glued-laminated timber beam connections reinforced perpendicular-to-wood grain with self-tapping screws (STS).Design/methodology/approachTwo full-size fire experiments were conducted on glulam beam-end connections loaded in flexure bending. Two connection configurations, each utilizing four steel bolts arranged in two different patterns, were reinforced perpendicular to wood grain using STS. The bolt heads and nuts and the steel plate top and bottom edges were fire protected using wood plugs and strips, respectively. Each connection configuration was loaded to 100% of the ultimate design load of the weakest unreinforced configuration. The test assemblies were exposed to elevated temperatures that followed the CAN/ULC-S101 standard fire time–temperature curve.FindingsThe experimental results show that the influence of the STS was significant as it prevented the occurrence of wood splitting and row shear-out and as a result, increased the fire resistance time of the connections. The time to failure of both connection configurations exceeded the minimum fire resistance rating specified as 45 min for combustible construction in applicable building codes.Originality/valueThe experimental data show the effectiveness of a simple fire protection system (i.e. wood plugs and strips) along with the utilization of STS on the rotational behaviour, charring rate, fire resistance time and failure mode of the proposed hybrid mass timber beam-end connection configurations.

Seismic fragility analysis and index evaluation of concrete-filled steel tube column frame-core tube structures

ABSTRACT To understand the effect of connection type on the seismic fragility of concrete-filled steel tube (CFST) column frame-core tube structures, typical structures with different numbers of storeys (15, 30, 45, and 60) and different types of beam-end connections (rigid connections, hinged connections, and rigid connections with outriggers) are designed. The probabilistic seismic demand models (PSDMs) of the structures are obtained using cloud analysis, and seismic fragility curves based on the mean period and the number of storeys are established. The results show that the differences in the seismic fragilities among the structures with the three types of connections can be effectively determined by the critical inter-storey drift ratio (IDR) and the storey ductility and that the determination method with the critical IDR is relatively simple. The use of beam-end hinges in the 15-storey structure results in an advantageous seismic performance, with a lower probability of exceeding the limit states, and the performance of the 60-storey structure with beam-end hinges is sensitive to spectral acceleration. The spectral acceleration and peak ground acceleration (PGA) can effectively describe the fragility curves based on the number of storeys and the mean period, respectively.

Non-linear FEA of mechanical properties of modular prefabricated steel-concrete composite joints

This paper study the seismic performance of modular prefabricated SRC column to steel beam composite joint (MPCJ) under static loading. Numerical modeling of MPCJs with three different beam-end connections was carried out in ABAQUS. Results of the numerical calculation were compared with existing quasi-static test results to verify the feasibility of the numerical model. The model was then used to analyze changes in the moment-rotation relation, failure mode, ductility, stiffness, and bolt stress in the joint between the column and joint module. Besides, stress distributions in the joints were analyzed along different stress paths. Under monotonic loading, the mechanical performance of the MPCJ is significantly affected by the beam end connection mode. Failure of the MPCJ mainly occurs at the beam end connection, thus, the aim of keeping the plastic hinge away from the joint core and preventing shear failure is achieved. Furthermore, the maximum story drift ratio is 3.9–5 times greater than the recommended limit, which indicates good ductility and deformation performance. The MPCJ of the three-beam end connection methods is all semi-rigid connections. The beam end structure will have a large influence on the bolt tension and stress distribution. According to the test research results, a nonlinear model with three parameters including joint cover plate cantilever section length, flange connecting plate thickness and flange connecting plate weld length was established. The theoretical calculation results was consistent with the results of the numerical simulation. MPCJs can be designed based on the proposed theoretical calculation formula.

Experimental study and numerical simulation of a new prefabricated SRC column to steel beam composite joint

This study investigated the influence of different beam end connection modes on the seismic performance of joints. Three prefabricated steel–concrete composite joints were tested by quasi-static test. Based on the experimental results, the refined finite element model was established by ABAQUS, and its reliability was verified. The influence of different parameters on the seismic performance of the joint was analyzed. The parameters include the length of the joint cover plate (lj), the thickness of the flange connection plate (tf), and the weld length of the flange connection (lw). The results show that different beam end connections significantly impact the seismic performance of the joint. The hysteresis curves of the three joints are relatively full, and the degradation performance of strength and stiffness is stable, thus achieving better energy dissipation capacity and ductility performance. Comparative analysis verified the correctness of the finite element model. lj has little influence on the bearing capacity and energy consumption, but has an obvious influence on ductility. tf and lw significantly influence the bearing capacity, ductility, and energy consumption of the joint. Under the influences of different lj, tf, and lw, the strength and stiffness degradation remain relatively stable.

Local web buckling of double-coped steel beam connections

This paper presents a comprehensive study on local web buckling behaviour of double-coped steel beam connections, cases which are common when beams of similar heights are joined. The study commenced with a series of full-scale tests on 11 specimens, covering a spectrum of cope lengths and cope depths. Local web buckling was observed as the main failure mode for most specimens. The ultimate load was found to decrease with increasing coped length and cope depth, and in addition, an increase of the rotational stiffness of the beam end connection could benefit the local web buckling capacity. A numerical study was subsequently performed enabling further interpretation of the test results. Good agreements were observed between the test results and finite element analysis predictions, and the stress conditions within the coped web panel at different loading stages were fully revealed. The numerical study also showed that the ultimate loads of some models were not sensitive to initial imperfection amplitudes, especially when the cope length was large (i.e. 450mm or longer). It was believed that the imperfection insensitivity characteristic was due to the presence of post-buckling mechanism. Summarising the available test data, including the current test results and those previously reported by other researchers, design comments were made through comparisons against the existing design method. Conservative test-to-predicted ratios were generally shown, but unsafe predictions were obtained for some cases. A modification to the existing design approach was finally proposed for safer design of such connections.

Experimental investigation of steel single plate beam end connections at elevated temperatures

This paper presents the results of a recently completed experimental research program on the performance of simple beam end framing connections at elevated temperatures. Connections are critical elements in maintaining the integrity of a structure during a fire, but the strength and deformation capacity of connections in fire are not well understood. In the US, one of the most common types of simple beam end framing connections is the single plate connection, which was the subject of this study.In this research investigation, a series of experiments were conducted on connection subassemblies at elevated temperatures to understand and characterize connection stiffness, strength, and deformation capacity, as well as failure modes. This paper first describes the testing facilities and procedures used for these experiments. The results of a series of tests are then described. The measured and observed performance of selected specimens is compared to the predictions from a finite element model, and the test results are also evaluated using simplified equations provided in the AISC Specification.

Studies on the Behavior of Steel Single-Plate Beam End Connections in a Fire

This paper summarizes the results of a recently completed research study on the behavior of simple beam end framing connections in steel buildings subjected to fire. Connections are critical elements in maintaining the integrity of a structure during a fire, but there are still many aspects of connection behavior in a fire that are not well understood. In the USA, one of the most common types of simple beam end framing connections is the single-plate connection, which was the subject of this study.In this research investigation, a series of experiments were conducted on connection subassemblies at elevated temperatures to understand and characterize connection stiffness, strength and deformation capacity, and to validate predictions of connection capacity developed by computational and design models. Three-dimensional finite element (FE) connection models were developed and these models were evaluated by comparing with experimental data. The FE models were then used to conduct an extensive series of parameter studies that investigated the impact of several key variables on connection response to the heating and cooling stages of a fire.This paper describes key aspects of this study, including the experiments, development of FE models and parametric studies. The paper highlights the results of the study that provide important insights into connection behavior during a fire and the implications of these results for design.

Experimental Examination of the Structural Performance of Restrained HSS Steel Beams and their End Connections in Fire

This paper describes a series of full-scale tests performed in the fire research facilities of Carleton University, Ottawa, Canada. These tests are part of an experimental programme, whose objective is to investigate the structural performance of axially restrained tubular steel beams at elevated temperatures. The primary focus is to determine the effect of the beam end connections on the structural performance of the steel-frame assembly. Four unprotected steel-frame test assemblies, each composed of a hollow structural section (HSS) steel beam restrained between two HSS columns, were subjected to a standard fire while constantly loaded. The main parameters investigated were the end plate thickness and the degree of beam axial restraint. Two different end plate thicknesses were tested, 12.7 mm and 19.0 mm. The experimental results showed a considerable effect of the end plate thickness on the structural behaviour of the connection and the connected beam. Moreover, the fire tests have revealed different connection failure modes, such as excessive end plate deformations, column buckling, and bolts fracture.

Study on the Static Characteristics of Web Connected Part of WBFW type Beam-End Connection

Study on the Static Characteristics of Web Connected Part of WBFW type Beam-End Connection

DISCUSSION ON RESEARCH ACTIVITY PUBLISHED AS “EFFECT OF ULTIMATE FLEXURAL STRENGTH OF BEAM END CONNECTION ON DEFORMATION CAPACITY Deformation capacity of welded beam-to-column connection subjected to repeated plastic strain Part 1”

DISCUSSION ON RESEARCH ACTIVITY PUBLISHED AS “EFFECT OF ULTIMATE FLEXURAL STRENGTH OF BEAM END CONNECTION ON DEFORMATION CAPACITY Deformation capacity of welded beam-to-column connection subjected to repeated plastic strain Part 1”

EFFECT OF ULTIMATE FLEXURAL STRENGTH OF BEAM END CONNECTION ON DEFORMATION CAPACITY

This paper presents results of full-scale cyclic loading tests under constant deformation amplitude conducted to evaluate deformation capacity of welded beam-to-column connection adopted in moment frames. Test specimens are designed and fabricated to investigate the influence of flexural strength of beam end connection. The deformation capacity expressed by the relationships between ductility and cumulative plastic deformation is revealed from test results. The relationships between crack growth at welded joint and strength of connection is evaluated regarding deformation amplitude. The initiation of crack is investigated about distribution of stress and strain obtained from FEM analysis.

CUMULATIVE DEFORMATION CAPACITY EVALUATION OF HIGH-STRENGTH STEEL BEAM ENDS SUBJECTED TO CYCLIC BENDING MOMENT

Structural system composed of high-strength steel frame with energy-dissipation elements is one of the suitable solutions for damage tolerant structure. In this concept, the main structure is designed in elastic zone for design earthquake level; however, there are still some risks to step into plastic zone in maximum considered earthquake levels. Because of high strength steel having high yield ratio, it is concerned to fracture early after yielding. In this paper, following the mock-up cyclic-loading tests and analysis of 800Mpa steel beam-column frame with diagonal BRBs, their fracture mechanism of beam-end connections are modeled using simple non-linear rotation springs, and estimation method for their cumulative energy dissipation capacities until their fractures in multistory structures are proposed.

Study on Designs to Prevent Fracture in Beam-to-Welded Box Column Connection Part2 Plastic Analysis of the Beam-End Connection

Study on Designs to Prevent Fracture in Beam-to-Welded Box Column Connection Part2 Plastic Analysis of the Beam-End Connection

Inelastic Behavior of Multistory Partially Restrained Steel Frames. Part I

This paper outlines the development of a finite element for use in the inelastic second-order analysis of partially (PR) and fully (FR) restrained planar steel frames. The finite element considers spread of plastification within the cross section and along the member length; centroidal shift of the elastic core; a variety of residual stress distributions; and P-Δ effects. Nonlinear spring elements are used in modeling beam-end connections. An arc-length technique (with iteration) is used in the analysis of individual beam-columns, while constant-work simple Euler stepping (no iteration) is used in the nonlinear analysis of frameworks. Full nonlinear load-deformation response of planar beam-columns and frames is computed. Accuracy is demonstrated through comparison with previously published analytical results. It is shown that concentrated plasticity models may lead to an overestimation of connection rotation in PR frameworks. A companion paper discusses the inelastic ultimate load analysis of large steel PR frameworks and evaluation of connection classification systems.

Distortion-induced fatigue cracking of bridge details with web gaps

Distortion-induced fatigue cracking from out-of-plane deformation in web gaps of bridge connection details is examined. This type of fatigue cracking results from interaction of various structural members during live loading of a structure and produces unanticipated distortion and high localized stresses. Although this type of problem is not confined to bridges, this paper focuses on bridge types and members that are susceptible to distortion-induced fatigue cracking at web gaps. This includes both plate-girder and box-girder bridges, as well as tied-arch bridges with box- and plate-girder members. Member details include transverse connection plates for cross-bracing and diaphragms, longitudinal gusset-plate details, and floor beam end connections. The crack development behavior is examined using field observations and measurements, as well as results from large-scale laboratory experiments. Recommendations for retrofitting distortion-induced fatigue damage are given, along with design alternatives to eliminate or minimize the occurrence of distortion-induced fatigue cracking.