Date of Award


Document Type

Master Thesis

Degree Name

Master of Engineering (Research)


Building & Civil Engineering

First Advisor

Mr. Martin P. Mannion

Second Advisor

Mr. John J. Murphy


The relative ease of design and construction of simple reinforced concrete beams provides an attractive option for structural engineering designers. However, where longer spans are involved it is more likely that prestressed concrete or possibly some form of steel beams will be preferred.

The primary cause of failure of longer span reinforced concrete beams is likely to be bending. However, the excessive deflection that might be associated with such beams must also be considered. When designing these beams, structural engineers make considerable use of span/effective depth ratios to select trial sections and check deflection limits. Such ratios are provided in the various structural design codes. However, as spans increase, and particularly where they exceed 10 metres, it may not be prudent to rely on simple span/effective depth ratios. Thus for longer span beams it is preferable to use deflections calculations to assess trial sections.

The purpose of this research was to consider longer span beams under incremental loading. The research considered how different aspects of behaviour - shear stress, shear strain, direct stress, direct strain and deflection - varied as the values of different input parameters - loads and beam dimensions - were changed. The finite element method of analysis was employed in the investigation. The software package LUSAS was used.

The decision of what constitutes a long span beam is a somewhat arbitrary one. Reference to concrete design codes of practice indicates that tables of basic span/effective depth ratios relate to spans up to and including 10 metres. For the research it was decided to consider a 50 % increase on this figure as an upper limit and to take a 20 % reduction as the lower limit. Thus spans from 8 to 15 metres were studied in conjunction with the concrete model and the LUSAS package.


Submitted to HETAC for the degree of Masters in Engineering (Structural).

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