George Clifton

Experimental Studies on Cyclic Performance of Column Base Strong Axis–Aligned Asymmetric Friction Connections

AbstractThis paper describes experimental testing of an asymmetric friction connection (AFC) at the base of a steel column such as may be used in a moment-frame. Friction/sliding surfaces were parallel to the column-strong axis. In-plane, out-of-plane and 2D clover leaf–cyclic tests were conducted of columns both with and without applied axial force. Tests were conducted both with and without bolts passing through the plates to provide compression on the sliding/friction interface. It was found that this type of rocking base–friction connection can tolerate high levels of drift without significant strength degradation, although some stiffness degradation occurred, especially after the cycles in the weak-axis direction. A simple procedure proposed to estimate the moment resistance is verified. The friction-base connections, having similar cost to conventional connections and exhibiting low-damage performance, have the potential to become widely used in aseismic construction.

Computer-aided Compliance Audit to Support Performance-based Fire Engineering Design

Computer-aided compliance auditing aims to provide an automated system to assess engineering designs against specified regulatory representations. Previous research has largely focused on prescriptive regulatory rules, which are relatively easier to audit than those pertaining to performance-based codes with qualitative criteria. There have been a few prototype implementations of rule-based compliance auditing systems that tend to represent regulatory knowledge as complex rule sets integrated into the system. The drawback of this approach is inflexibility, relatively high costs and dependency on the system programmer to modify built-in rules in response to on-going regulatory amendments. The current research looks at representing regulatory knowledge as a library of compliant design procedures (CDP) and the associated regulatory rules, which are treated as external input components to the system. This would allow them to be managed and maintained independently by designers and regulators as appropriate experts in their respective fields. This paper reports on the development of a computable regulatory knowledge model (RKM) that can be used in conjunction with a CDP to audit an object-based building information model (BIM) automatically. CDPs can be described graphically as workflows in the open standard Business Process Model and Notation (BPMN), which can be executed to automate the compliance audit process. A RKM representing the fire engineering performance-based verification method prescribed by the New Zealand Building Code is proposed for use by a set of CDP workflows to automatically audit the design for compliance. The potential of interfacing with simulation tools to provide some of the required input parameters is discussed.

Slab Effects on Beam-Column Subassemblies - Beam Strength and Elongation Issues

This paper describes the effect of composite slabs in increasing beam strength and its implications for design. It also discusses the “beam-growth” phenomena, which can detrimentally influence the performance of a frame with reinforced concrete or precast concrete beams, and its impact on steel beams with RC slabs. From the subassembly testing conducted the slab increased the beam strength by around 40%. However the slab could not maintain strength at large drifts without degradation with transverse or longitudinal decking placed around the columns. This indicates that while transverse or longitudinal slabs should not be considered in design to size the beam, they should be considered in the beam overstrength calculations for the design of other members. Also, both rational considerations and experimental results

Fire Performance of an Office Building with Long-span Cellular Floor Beams—Britomart East, Auckland

Abstract This paper presents the application of a structural fire model to a twelve-storey office building in Auckland, which was one of the first projects in New Zealand to use long-span cellular floor beams. The structural fire model that was employed is known as the slab panel method (SPM), which is an extension of the Bailey tensile membrane model. Owing to the fact that the cellular beams had been optimised for structural efficiency, there was little reserve of strength in fire conditions, which resulted in the SPM predictions of peak deflection being supplemented by finite element simulations for a range of design fire severities. The simulations indicated that there was a tendency for the bottom flange of the asymmetric cellular beams to displace laterally, which resulted in the beams that form the slab panel supports requiring vertical stiffeners. Nevertheless, from these analyses it was demonstrated that the passive fire protection could be eliminated from the long-span secondary beams, with only the elements critical to the structural stability of the floor requiring applied fire protection. The resulting 80% reduction in the passive fire protection on the long-span cellular beams led to cost savings in excess of NZD 300 000 (EUR 189 000) to the client.

Portal Frames with a Novel Cold-Formed Tapered Box-Section

This paper introduces a novel steel portal frame system, in which cold-formed nested tapered box members are used in the design. The bird and dust proofing features of the system make it useful for applications where clean work areas are required, such as food, storage, and manufacturing industries. The new section used in the portal frames comprises two cold-formed channels welded to each other, forming a box-shaped steel member, either tapered or prismatic along its length. Such sections possess high torsional stiffness compared with the conventional I-sections; therefore, lateral bracing employed for the flexural-torsional buckling suppression of I section portal frames is mostly unnecessary. A comparative study, taking into account the cost of steel, painting, bird proofing and lateral bracing, is conducted between a number of portal frames with the proposed box-sections and the conventional I-sections. An analysis and design code, incorporating the Genetic Algorithm (GA), is developed to optimise the weight of the designed frames. The results indicate that the novel portal frame system is economically viable with additional benefits of bird and dust proofing. To investigate the failure modes and verify design procedure of the new portal frame, an experimental testing program is undertaken in University of Auckland. The test results show excellent behaviour and good agreement with the numerical models but have been completed too recently to be included in this paper.

Braced Frame Symmetrical and Asymmetrical Friction Connection Performance

This paper describes quasi-static testing of Asymmetrical Friction Connection (AFC) and Symmetrical Friction Connections (SFC) in steel braces. It is shown that stable energy dissipation mechanisms have been achieved in braces using Bisalloy 500 shims on the sliding surface. When incorporated into a moment frame, the braces and the moment resisting frames underwent large displacements without significant frame yielding. The effective coefficient of friction is shown to be dependent on prying.

Analytical Methodology to Predict the Beam Overstrength Considering the Composite Slab Effects

The design strength of moment resisting steel frames in seismic regions around the world is generally calculated without considering strength enhancement caused by the slab. For column and panel zone design in New Zealand, the beam overstrength including the slab effect is considered. If the slab could be detailed to provide reliable lateral force resistance, then considering it directly in design would result in smaller beam sizes and more economical steel frames. In this paper, a simple analytical model (considering all key modes of failures) to predict the variation in strength due to the presence of the slab is proposed and validated with the experimental data. The proposed model to develop dependable slab contributions may change the design of steel moment frames around the world.

The Sliding Hinge Joint: Final Steps towards an Optimum Low Damage Seismic-Resistant Steel System

The Sliding Hinge Joint with Asymmetric Friction Connectors (SHJ), to give its full name, is a semi-rigid moment resisting joint used between the beams and columns of a moment-resisting steel frame and also at the column base between the column and the ground. It’s performance is intended to be as follows: 1) On completion of construction, rigid under serviceability limit state conditions, 2) During a severe earthquake, allowing controlled rotation between the column and the beam or foundation on designated friction sliding planes within the connection, then 3) Returning to its rigid in-service condition at the end of the severe shaking with the building returning to its pre-earthquake position (self-centering). During its development and proof of concept through large scale testing, the initial results showed that the SHJ as originally designed and detailed performs 1) and 2) very well, but the bolts in the friction sliding planes loose much of their original installed bolt tension during significant sliding, lowering the level at which rotation within the joint will occur post severe earthquake. A concerted research programme of component testing, analytical model development and numerical modelling in recent years has developed solutions to the bolt tension loss issue as well as enhanced the joint’s performance to deliver dependable self-centering capability for the building. This work marks the final steps towards developing an optimum low damage seismic-resisting steel moment frame system. This paper presents key findings from the research work and general recommendations for the optimum performing sliding hinge joint.

Seismic Tests of Welded Moment Resisting Connections Made of Laser-Welded Stainless Steel Sections

Steel structures are well established as the preferred material for constructing seismic resisting systems in New Zealand and around the world. While the majority of steel framing is made of carbon steel, stainless steel is increasingly being considered for designing exposed steel structures. Because of significant differences in the mechanical properties between the two materials, seismic resisting system design rules for connections between carbon steel members may not be applicable, at least without modification, to connections between stainless steel members. This study has investigated the seismic performance of welded T-shaped beam-column moment resisting connections made of structural stainless steel beams and columns manufactured by laser welding. The paper included the results of three large-scale T-shaped specimens, of varying sizes, subjected to seismic loads. The grade of laser-fused stainless steel was 304 L and its specification was according to ASTM A276. The sections were subject to the seismic tests in accordance with the SAC protocol given in ANSI/AISC 341-10. The results shows substantial amount of energy dissipation by welded moment resisting stainless steel connections along with a high ductility capability and dependable behaviour in the inelastic range.

Experimental Testing and Design of High Performance Shear Links for Eccentrically Braced Frames

Steel links inside Eccentrically Braced Frames (EBFs) can be classified as either short, intermediate or long. The more commonly used short links yield primarily in shear and dissipate incoming energy inside the web of the link. Advances in shear link research and industry practice, particularly the increased use of bolted links, have allowed greater freedom in the design of the link section, as the section used can be decoupled from the collector beam section. Seven shear link specimens were tested inside a full scale EBF set up, and were subjected to AISC’s 2005 shear link loading protocol. Increasing levels of rotation were applied to links of varied cross-sections and intermediate stiffener spacings. Links with low web aspect ratios performed to a higher rotation than past research would have suggested, and when intermediate stiffeners were removed, they performed to an even higher rotation. Recommendations for design are presented, including a relaxation of the stiffener spacing equations when web aspect ratio criteria are met. A provision is also included to allow greater rotational ductilities in EBF frames with low web aspect shear links.