Partial-strength Connections Research Articles

Limiting the sway on multi-storey un-braced steel frames bending on weak axis with partial strength connections

This paper investigates the design using wind-moment method for semi-rigid un-braced steel frames bending on weak axis. A limiting sway method has been proposed to reduce the frame sway. Allowance for steel section optimization between moment of inertia on minor axis column and major axis beam was used in conjunction with slope-deflection analysis to derive equations for optimum design in the proposed method. A series of un-braced steel frames comprised of two, four, and six bays ranging in height of two and four storey were studied on minor axis framing. The frames were designed for minimum gravity load in conjunction with maximum wind load and vice-versa. The accuracy of the design equation was found to be in good agreement with linear elastic computer analysis up to second order analysis. The study concluded that the adoption of wind-moment method and the proposed limiting sway method for semi-rigid steel frame bending on weak axis should be restricted to low-rise frames not more than four storey.

Experimental Investigation on Slip-In Connection for Cold-Formed Steel Double Channel Sections

The application of cold-formed steel in light steel framing design can become a popular choice of Industrialized Building System, by moving huge amount of construction work to the factory and leaving the construction site cleaner and safer. However the joints behaviour for primary structures, particularly the partial strength semi-rigid beam-to-column connection has not been studied in depth. This paper presents the isolated joint test on slip-in connection using 6 mm hot-rolled steel gusset plate. Two cold-formed lipped channel sections were placed back-to-back to form beam and column members. Three specimens with the depth of beam ranging from 150 mm to 250 mm were tested. From the experimental results, it is observed that the ratio of moment resistance of joint to the moment resistance of the connected beam increases in the range of 0.46 to 0.70. The rotational capacities of the joints exceed 30 mRad. The rotational stiffness achieves 511 kNm/rad to 1671 kNm/rad. It is concluded that the proposed connections could be classified as partial strength connection.

SHAPE AND SECTION OPTIMIZATION FOR FREE-FORM STEEL STRUCTURES CONSIDERING CONNECTION COST

A shape and section optimization method is presented for free-form steel structures considering cost of connections. Two types of rigid connections are considered. One is a conventional full-strength connection, and the other is a partial-strength connection using for example fiber reinforced mortar. The inherently different costs of the two are made continuous by introducing a cost increase function of the latter. A nest-structure optimization, consisting of a shape and section optimization as the main problem and cost minimization of each connection as the sub-problem, is proposed to minimize the total cost of members and connections. Examples of a single-layer lattice roof are shown to demonstrate the effectiveness of the proposed method.

Cyclic behavior and numerical modelling of a semi-rigid frame

It is clear that semi-rigid frames exhibit completely non-linear behaviour under cyclic loading due to gradual yielding of connection components. The current study presents the experimental results from the test of a semi-rigid frame specimen, comprising a single storey and one bay, and the analysis results obtained from a finite element model of the specimen. In this study, semi-rigid joints with header plates are used for beam-tocolumn connections. The initial stiffness and moment-carrying capacity of the connection, designed as a semi-rigid and partial strength connection type, were determined in accordance with Eurocode 3. In the modelling of the semi-rigid beam-to-column connection behaviour, four-parameter non-linear representation of the moment—rotation curve obtained using the Ramberg-Osgood formula was employed. Loading of the test specimen consisted of quasi-static cycles with displacement control. The cyclic response of the specimen is characterized by a stable hysteretic behaviour. When comparing the envelope of the hysteresis loops from the cyclic test of the specimen with the pushover curve achieved by non-linear finite element analysis, the model gives a good prediction of the ultimate strength and initial stiffness of the frame.

Dynamic response of composite frames with different shear connection degree

The influence of partial composite action between concrete slab and steel beam and of partial-strength connections on the seismic response of composite frames is evaluated. To this end, experimental tests were carried out at the Laboratory of the National Technical University of Athens. The specimens, one-story one-bay moment-resisting frames with steel–concrete composite beams, were tested under base acceleration on the shaking table. Experimental results demonstrated that for different degrees of partial interaction between the slab and the beam the response of the specimens varied significantly. Specimens with intermediate and low shear connection degree showed the most favourable performance, in terms of ductile behavior and energy dissipation. The slip between the slab and the beam interface contributed to the energy dissipated by the system and the ductility demands decreased on other parts like the beam ends and the joints. Then, finite element models simulating the behavior of the tested specimens were developed and, after validation, extended parametric studies were carried out. The main objective is to investigate the influence of the partial interaction and the employment of partially restrained beam-to-column joints on the dissipative capacities of composite frames under strong ground motions. Numerical results confirmed the experimental conclusions and revealed that the use of intermediate and low shear connection degrees with partial-strength joints results in an advantageous seismic design.

Comparison of component method with experimental tests for flush end-plate connections using hot-rolled perwaja steel sections

A component method has been introduced by Steel Construction Institute to predict the moment resistance of partial strength connection. The design philosophy is taken directly from Eurocode 3 with strength checks on bolts, welds, and steel which have been modified to comply with BS 5950-1:2000. The accuracy of the method however needs to be validated with the experimental tests especially for hot-rolled sections other than typical British Section (BS). Six experimental tests on beam-to-column connections have been carried out for Flush End-Plate (FEP) connections consisting of variable parameters such as thickness of end-plate, size and number of bolts, size of columns, and beams. The tests were set-up using local hot-rolled steel sections known as Perwaja Section (PS) for beams and columns instead of typical British Section (BS). The strength of materials for end-plate, column and beam sections were tested for tensile strength and used in predicting the moment resistance for component method. The moment versus rotation of the test results were plotted and compared with the moment resistance derived from component method. The study concluded that the moment resistance of the tested flush end-plate connections was higher than the predicted moment resistance from component method which showed good agreement between the two moments. The study also concluded that the tested FEP connections met the requirements and criteria of partial strength connections.

Seismic performance of a 3D full‐scale high‐ductility steel–concrete composite moment‐resisting structure—Part I: Design and testing procedure

AbstractA multi‐level pseudo‐dynamic (PSD) seismic test programme was performed on a full‐scale three‐bay two‐storey steel–concrete composite moment‐resisting frame built with partially encased composite columns and partial‐strength connections. The system was designed to provide strength and ductility for earthquake resistance with energy dissipation located in ductile components of beam‐to‐column joints including flexural yielding of beam end‐plates and shear yielding of the column web panel zone. In addition, the response of the frame depending on the column base yielding was analysed. Firstly, the design of the test structure is presented in the paper, with particular emphasis on the ductile detailing of beam‐to‐column joints. Details of the construction of the test structure and the test set‐up are also given. The paper then provides a description of the non‐linear static and dynamic analytical studies that were carried out to preliminary assess the seismic performance of the test structure and establish a comprehensive multi‐level PSD seismic test programme. The resulting test protocol included the application of a spectrum‐compatible earthquake ground motion scaled to four different peak ground acceleration levels to reproduce an elastic response as well as serviceability, ultimate, and collapse limit state conditions, respectively. Severe damage to the building was finally induced by a cyclic test with stepwise increasing displacement amplitudes. Copyright © 2008 John Wiley & Sons, Ltd.

Structural Behaviour of Trapezoidal Web Profiled Steel Beam Section using Partial Strength Connection

Connections are usually designed as pinned which associated with simple construction or rigid which is associated with continuous construction. However, the actual behaviour falls between these two extreme cases. The use of partial strength or semi-rigid connections has been encouraged by EC3 code and studies on hot-rolled steel sections on semi-continuous construction for braced steel frames have proven that substantial savings in steel weight and the overall construction cost. The objective of this paper is to present the performance of full scale testing of sub-assemblage steel beam and isolated beam-to-cloumn with partial strength connections for Trapezoid Web Profiled (TWP) steel sections. The TWP steel section is a built up section where the flange is of S355 steel section and the corrugated web of S275 steel section. Two full scales testing with beam set-up as sub-assemblage and beam-to-column connection have been carried out for flush and extended end-plate connections as partial strength connections. It was concluded that the use of extended end-plate connection has contributed to significant reduction to the deflection and significant increase to the moment resistance of the beam than flush end-plate connection.

Experimental analysis and modelling of bolted T-stubs under cyclic loads

Bolted connections have recently attracted new research efforts after the unexpected failures of welded connections during Northridge and Kobe earthquakes. The criteria and the formulations for predicting the rotational stiffness and the flexural resistance, under static loading conditions, of the most common connection typologies have been codified by Eurocode 3 [CEN. EN 1993-1-8 Eurocode 3: Design of steel structures — Part 1.8 Design of joints. 2005] which is based on the so-called component approach. In order to extend the component approach to the prediction of the seismic response of partial-strength connections, the modelling of the cyclic response of the joint components is necessary. Starting from the observation that the main sources of deformability and plastic deformation capacity of bolted connections can be modelled by means of an equivalent T-stub, an experimental program devoted to the cyclic response of the most important component of bolted connections has been carried out aiming at the modelling of the cyclic force–displacement curve of bolted T-stubs. In this paper, starting from the analysis of the results of the experimental tests performed, stiffness and strength degradation rules are derived as a function of the displacement amplitude required at any cycle and of the energy dissipated in the previous loading history. The combination of these rules with the theoretical prediction of the monotonic envelope leads to a proposal for predicting the cyclic behaviour of bolted T-stubs starting from the knowledge of their geometrical and mechanical properties.

Experiment Investigation on Failure Behavior of Partial-Strength Connections with Column Skin Plate Deformation

Experiment Investigation on Failure Behavior of Partial-Strength Connections with Column Skin Plate Deformation

SEISMIC DESIGN OF STEEL FRAMES WITH PARTIAL STRENGTH JOINTS

In the seismic design of steel frames, beam-to-column joints can be designed either as full strength joints, forcing the location of the plastic hinges at the beam ends, or as partial strength joints which have to dissipate the seismic input energy. Seismic codes provide specific design criteria for full strength joints, but there are no detailed recommendations dealing with partial strength connections. Therefore, in this paper, by means of a simplified model, such as a SDOF system, the requirements which partial strength joints have to possess, for designing steel frames characterised by seismic performances equivalent to those of steel frames with rigid full strength joints, are pointed out. Successively, starting from the above requirements, a new method for designing seismic resistant steel frames with extended end plate connections leading to the complete definition of the geometrical and mechanical parameters of the joints is proposed.

The effects of partial shear connection in composite flush end plate joints Part I — experimental study

The experimental results of partial shear connection composite beams subjected to hogging bending have been previously reported. An extension to this work which considers the presence of a semi-rigid, partial strength connection is described herein. Five sub-assemblages of cruciform composite joints that simulate the internal region of a semi-continuous frame were tested. The joints were constructed using a novel approach of blind bolting a flush end plate to concrete-filled square hollow columns. Apart from the level of shear connection, the other parameter varied was the reinforcement area. In addition, a bare steel joint was also tested to act as comparison specimen. Based on the experimental results, the intrinsic behaviour of the joints in terms of strength, stiffness and ductility was assessed. It was further affirmed that by lowering the levels of shear connection, the rotation capacity of the composite joints was enhanced with only a slight compromise if the stiffness and moment resistance. A notable effect on the connection behaviour was also observed by varying the reinforcement levels. The outcomes clearly affirmed the benefits of partial shear connection in contributing the additional flexibility to increase the joint ductility, which is extremely advantageous for plastic design purposes. In view of this, the current restriction of providing full shear connection design within hogging moment regions of continuous and semi-continuous structures could be relaxed.

Prequalification of Steel Moment-Frame Connection Performance

Welded-flange/bolted-web connections were damaged during the Northridge earthquake, and the SAC Steel Project was funded by the Federal Emergency Management Agency to find solutions to the problems caused by this damage. The Connection Performance Technical Advisory Panel was one of several groups completing the project research, and this group examined all connection performance issues. Many connections were evaluated, and some were prequalified for future use without detailed testing or evaluation. This prequalification criteria and the methods used to satisfy the criteria are described. Some connections that satisfy the prequalification criteria are summarized and the general basis for the prequalification limits are noted. Prequalification requires an adequate experimental database for understanding and evaluating all yield mechanisms and failure modes for each connection type. The concept of the yield mechanisms and failure modes, and the application of the experimental data toward meeting the prequalification requirements are described. A wide range of connections including fully bolted connections, welded connections, and a range of partial-strength and partial-stiffness connections are included.

Strength and rotational stiffness of simple connections to tubular columns using flowdrill connectors

A new thermal drilling technique (the flowdrill process) has made it possible to use ordinary bolts in tapped holes in relatively thin-walled tubes. This in turn has opened the opportunity for traditional partial depth and flush endplate connections to be used to join open section beams to tubular columns in simply designed braced steel frames. The experimental work reported concerns a series of tests conducted to investigate the moment capacity and rotational stiffness of simple joints bolted to tubular columns using flowdrill connectors. Tests show the connections to behave in a manner suitable for use as either pinned or partial strength connections for simply designed braced steel frames. This paper is one of a series; the others deal with moment-resisting connections and the influence of filling the tubes with concrete.

Design Guide for Partially Restrained Composite Connections

Partially restrained composite connections (PR-CC) are partial strength connections that can be used to resist moments induced by live, wind, and earthquake loads in low and moderate height unbraced frames. PR-CC use the continuity and strength that are already built into the structures and are especially well suited for low-rise structures in areas of low-to-moderate seismic risk. Good hysteretic performance was the primary criterion used in the development of the analysis procedures and design criteria presented in this guide. These procedures are more detailed and conservative than those in the 1997 National Earthquake Hazards Reduction Program and American Institute of Steel Construction seismic specifications and apply to a wider range of structures. Trial designs indicate that the most efficient structures result when connection strength is about 75% of the noncomposite strength of the steel beams framing into the connections.

Design rules for beam-to-column connections in Europe

Abstract For many years, research on welded and bolted beam-to-column connections has been carried out with particular emphasis on semi-rigid and partial strength connections. Using these types of connection allows for a wide range of moment distributions in frames and gives the possibility of optimizing the cost of the construction by balancing the material cost of the members against the labour costs of the connections. The appropriate design rules for unstiffened welded and bolted connections are discussed.