The non-linear analysis of masonry arches.

The objective of the research programme has been to investigate the problems besetting the national masonry arch bridge stock and topropose enhanced means of appraisal accordingly. The programme has involved site assessments and limited experimentation together with limit state and serviceability analyses. All theoretical and empirical studies have been mounted as micro-computer software and are supported by computer graphics. Throughout, the accent is on engineering requirements in practice; the almost universal absence of as-built drawings and the involvement of natural materials whose mechanical properties are highly variable are to be noted from the outset. Initial considerations relating to the arch form, its historical context and present masonry arch assessment methods are set out in Chapter 1. Fieldwork studies are presented in Chapter 2. The concept that masonry has finite compressive strength isaccordingly considered in Chapter 3 which includes experimentation establishing the appropriate constitutive properties with respect to natural rock. A general moment-thrust response modelling is established and an original non-linear limit-state moment-thrust interaction diagram is determined. Limit state and serviceability masonry arch bridge models ofinnovatory form are included in Chapter 4. These models follow from the studies of Chapter 3 and are novel in their own right. However, the critical arguments upon which they are based demand that these models be seen as prototypes of enhanced models whose features have now been established. Overall conclusions are discussed in Chapter 5 wherein the practical factors affecting the nature of masonry arch bridges are juxtaposed with the engineering requirements imposed upon them. Modern assessment methods must afford output that is safe without being overconservative. The findings of the research programme are in keeping with this. Supporting documentation is given in the Appendices

A comparison of opiate- and epidural-induced alterations in splanchnic blood flow using intra-operative gastric tonometry

Several methods are available to measure splanchnic blood flow and gut ischaemia. Tonometry is most practical for peri-operative use. Epidural blockade from T5 to T11 causes mesenteric arteriovenous vasodilation and may increase splanchnic blood flow. This study assesses the ability of tonometry to measure differential effects of opiate and epidural analgesia on splanchnic blood flow. Forty patients for elective colorectal surgery were randomly allocated to receive epidural infusion or intravenous morphine. Gastric mucosal PCO2, pHi, standard pHi, PCO2 gap and pH gap were measured after induction and on termination of surgery. These parameters were within normal limits at the end in most cases and there was no significant difference between the groups. The complication rate was similar in both groups and was not correlated with low pHi, but was correlated with blood loss. We were unable to demonstrate a difference in splanchnic perfusion, as assessed by gastric tonometry, between the two groups