Research

Steel-concrete composite beams using precast hollow-core slabs and a demountable shear connection mechanism (2016 - 2018; Funded by the EPSRC)

Composite construction of steel and concrete is the most efficient structural solution for buildings and bridges. Composite beams are currently constructed using headed shear studs welded to the steel beam and embedded to the concrete slab in order to exploit the advantages in strength and stiffness offered by the composite action. This construction method, however, eliminates the possibility for deconstruction and reuse of the materials of composite floor systems. This project will explore a new shear connection system for composite floors. The proposed system will combine the advantages that composite construction and precast hollow core slabs provide, while it will introduce a novel, demountable shear connection mechanism between the slab and the beam, realising an easily 'deconstructable' structural system. The proposed structural system aims at addressing the urgent need for reduction in CO2 emissions and waste products in the construction industry.

Explicit fracture simulation of duplex stainless steel dampers used in resilient steel frames (2015-2016)

The use of steel dampers with high post-yield stiffness as the main energy dissipating system in braced frames resulted in a significant reduction of residual drifts after strong earthquakes. The dampers are hourglass-shaped pins made of duplex stainless steel. This project evaluates the cyclic behaviour of the proposed dampers both experimentally and numerically. Two different geometries of full-scale prototype dampers were tested under various standard and random cyclic loading protocols in a configuration that reproduced the damper-brace connection in the actual steel frame. The results of fourteen tests showed that the proposed dampers possess excellent hysteresis and fracture capacity. Following the tests, explicit numerical simulations were carried out using the Abaqus software. Geometry-independent fracture criteria were calibrated using the results of monotonic and cyclic tests on coupon specimens made of duplex stainless steel and explicitly included in the numerical simulations of the dampers. The finite element models are able to accurately capture the initiation and evolution of fracture in the prototype dampers subjected to both standard and random cyclic loading histories. The results can be used to calibrate reliable macro-models for seismic collapse simulations of the proposed frame.

Minimal-damage steel and composite column bases (2013 - 2016)

Column base connection (consisting of the column, the connection system, and the anchorage to the foundation) is one of the most important components of steel moment-resisting frames (MRFs) or braced frames (BFs). The current seismic design methodology, however, results in considerable damage at the steel column bases under the design earthquake, which affects the structural performance of MRFs or BFs. Moreover, conventional typologies are costly to fabricate and cannot be easily repaired or deconstructed if required.

This project will develop a novel type of steel column base connection that will have the potential to be easily repaired after the design earthquake by concentrating the damage in replaceable energy-dissipating 'fuses'. In addition, the connection will provide the option for easy deconstruction and reuse of its components at the end of the service life of the building. The project will include both experimental work and advanced numerical simulations of the proposed column base connection. Emphasis will be given in developing a reliable design procedure for the new column base connection within the frameworks of Eurocodes 3, 4 and 8.

Steel energy-dissipating devices made of high-performance steel (UWS, 2012 - 2013)

Steel yielding hysteretic devices provide a reliable way to increase the energy dissipation capacity of structures under seismic loading. Steel cylindrical pins with hourglass shape bending parts (called web hourglass shape pins - WHPs) have been recently used as the energy dissipation system of post-tensioned connections for self-centering steel moment-resisting frames. This project evaluated the cyclic behavior of WHPs made of high-strength steel and two grades of stainless steel, i.e. austenitic grade 304 and duplex, through twenty-six tests using different cyclic loading protocols and different WHP geometries. The tests showed that WHPs have stable hysteretic behavior and high fracture capacity. WHPs made of stainless steel exhibited excellent ductility under cyclic loading. Duplex stainless steel showed the most favorable behavior for seismic design and, thus, this material is recommended for the construction of sacrificial energy-dissipating devices in seismic-resistant structures.

Shear strength and moment - shear interaction in steel-concrete composite beams (UWS, 2011 - 2012)

Composite beams are often subjected to combined bending and shear loading; however, current structural codes do not provide design models for the shear strength and moment-shear interaction in composite beams. This project aimed to evaluate the shear strength and moment-shear interaction in steel-concrete composite beams through an extensive experimental and numerical study. Fourteen simply-supported composite beams and one steel beam were tested under combined bending and shear. The effects of partial shear connection and shear reinforcement in the slab were also studied. A nonlinear finite element model was developed and found capable of accurately predicting the strength and stiffness of the composite beams. Extensive parametric studies were conducted using the validated numerical model. The results allowed for the derivation of a moment-shear interaction law for composite beams and highlighted the high degree of conservatism in the current structural provisions. It is shown that both the concrete slab and the composite action contribute significantly to the shear strength of a composite section and that the main factors that influence the shear capacity of a composite beam are the slab thickness and the degree of shear connection. Based on the experimental and numerical results, a design model is proposed for a more efficient design of composite beams in regions where the acting shear is high.

Self-centering steel post-tensioned beam-column connections with web-hourglass pins (UWS, 2010 - 2012)

This project proposed and validated a new self-centering beam-to-column connection. The connection uses post-tensioned high-strength steel bars to provide self-centering capability and carefully designed energy-dissipation elements that consist of steel cylindrical pins with hourglass shape, namely the WHPs. Pilot tests on WHPs have shown that they possess high energy dissipation and fracture capacity. WHPs are placed between the upper and the bottom flanges of the beam so that they do not interfere with the composite slab. A simplified performance-based procedure was used to design the proposed connection. The connection performance was experimentally validated under quasi-static cyclic loading. The specimens were imposed to drift levels beyond the expected design ones to identify all possible failure modes. The experimental results show that the proposed connection eliminates residual drifts and beam damage for drifts lower or equal to 6%. A simplified analytical procedure using plastic analysis and simple mechanics was found to accurately predict the connection behavior. Repeated tests on a connection specimen were conducted along with replacing damaged WHPs. These tests showed that the WHPs can be easily replaced without welding or bolting, and hence, the proposed connection can be repaired with minimal disturbance to building use or occupation in the aftermath of a major earthquake.

Behavior and design of steel-concrete composite beams under bending and axial loading (UWS, 2010 - 2012)

Steel-concrete composite beams are often subjected to combined bending and axial loading. However, current structural provisions do not cover the behavior of composite beams under combined actions; they rather refer the designer to the specifications for steel structures. This project aimed to provide design guidance for composite beams under combined actions. An extensive experimental program on full-scale composite beam prototypes subjected to both positive and negative bending and both compressive and tensile axial forces was first carried out. Detailed finite element models were also developed and used to generalize the experimental results. Based on the results of the tests and the numerical analyses, simplified design models are proposed for use in practical design of composite beams.