Author: Gregson, S J
First published: N/A
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Gregson, S J
Load - strength charts have proved useful for preliminary sizing of members in pitched roof portal frames. They also provide an independent means of checking simple plastic collapse strength derived from computer analysis. Unlike previous charts, those presented here allow for the effect of partial column base restraint and enable the minimum length of eaves haunch to be determined directly. The new charts are applicable to a wide range of frame geometry and rafter/column strength ratios. Nominal base restraint is often used in the UK to prevent inward collapse of frames and consequent damage to external walls, in the event of a fire. More substantial restraint can also be used to improve sway stability and eaves deflection. The basis of the charts is defined and may be incorporated into a more direct computer-aided design scheme if desired, but the real intention of the charts is to provide a computer-independent means of determining member sizes. Three examples of their use are given. The first sets out with preconceived rafter/column strength ratio, assuming pinned bases. The second imposes a restricted set of preferred sections, also using pinned bases, and seeks to improve on the previous total weight of steel. In the final example, use of base restraint equivalent to 20% of the column plastic moment leads to a further 7.5% saving in total weight of steel.
J.O. Surtees and S.H. Yeap
The University of Sheffield has a significant and long-standing reputation for research into the behaviour of cement, concrete materials technology and reinforced concrete design and analysis. In recognition of this work, a new research unit, the Centre for Cement & Concrete (CCC), was launched on 1 August 1993. This unit comprises 15 academics from the Departments of Civil & Structural Engineering, Mechanical & Process Engineering, Engineering Materials, Earth Sciences, and Architectural Studies. The Centre is run under the directorship of Professor Peter Waldron (M) (Head of the Department of Civil & Structural Engineering) and management of Dr Roger Crouch. In addition to the academic staff, the Centre benefits from a close association with Dr David Lawrence and Professor David Spooner of the British Cement Association (BCA), both honorary members of the Centre. There are currently over 35 postgraduate students and research associates (excluding Masters students studying Concrete Engineering) working in the CCC. Thus the Centre represents one of the largest research organisations of its kind. Whilst it would be inappropriate to list all areas of activity, the following gives some indication of the range of investigations currently under way.
Dr R.S. Crouch
A two-storey precast concrete framed ofice block dating from the 1960s was found to have high alumina cement (HAC) concrete beams at roof and first-floor levels. Detailed investigation showed that the first-floor beams were satisfactory but those at roof level could not be proved. In addition, problems were found with first-floor corbel details and the precast frame beam-column joints. Because the ground floor area had to remain in use during repairs and also the foundation conditions were poor; the roof
was strengthened from above using ‘skyhooks’ - steel beams placed over it and preloaded to limit stresses in the HAC beams. The first-floor corbels were strengthened by drilled-in prestressed bars.