Timber Bridges - Design and Appropriate Use of Materials

Lateral-torsional buckling of beams Richard Harris, from Bournemouth, has examined the eflective length of compression flanges of - as he describes it - ‘(not so) simple beams’ and continues: This subject causes much confusion. If we, as a profession, cannot even agree on the design of simple beams, we do not deserve the respect from the public that so many of us apparently want. Unfortunately, the guidance on effective length in the various British Standards relating to structural steelwork elicits no uniform response from practitioners. I do not think thathis should be blamed on ‘engineering judgment’. There are two aspects, each of which is often treated differently by various designers: (i) does the compression flange have sufficient restraint to prevent lateral-torsional buckling? (ii) if not, what is the effective length of the flange? SCI publication Lateral Stability of Steel Beams and Columns, gives excellent guidance.

Robustness tests have been undertaken on a full-scale six-storey timber frame test building. The building, known as TF2000, is the result of a DETR-supported and industry-funded research project. The core research programme includes full-scale tests to enable an evaluation of the actual behaviour of the TF2000 structure when selected vertical loadbearing wall panels are removed. This evaluation was to verify by ‘test’ that the inherent stiffness of standard cellular platform timber frame construction can provide adequate robustness so that, in the event of an accident or misuse, the building will not suffer collapse to an extent disproportionate to the cause. This is referred to as disproportionate collapse compliance within the UK Building Regulations. M.W. Milner, S. Edwards, D.B. Turnbull and V. Enjily

Greater use of factory prefabricated components is increasingly being recognised by the construction industry as a means of improving productivity and fulfilling customer requirements. The significance of this approach to construction is recognised in Sir John Egan’s recent report ‘Rethinking Construction’ for DETR. Adoption of prefabricated products delivers benefits via overall project cost reduction, faster construction times, reduced material waste and fewer call-backs. The application of this trend to floor construction is evident in timber prefabricated floor assemblies and kit-based systems. This feature reconsiders timber as a component in floor systems, and illustrates the potential for improvement, drawing upon prefabrication and variation of construction forms away from the traditional. The principles of reengineering the business process have been used, focusing on industry competitiveness, cost-efficient supply-chain management, and satisfaction of customer needs. This feature is the result of work supported by the Department of the Environment, Transport & the Regions (DETR), TRADA, Guildway Timber Structures, and TRADA Technology. M.W. Milner and R.J. Bainbridge