Ezzeldin Y. Sayed-Ahmed

NUMERICAL INVESTIGATION INTO STRENGTHENING STEEL I-SECTION BEAMS USING CFRP STRIPS

Fibre Reinforced Polymer (FRP) strips offer an economic strengthening alternative for steel I-beams. Investigations are currently limited to applying FRP strips to the tension flange of the I-section to increase its flexural strength. However, for thin walled “slender” I-section steel beams, the risk of buckling failure is also a major concern. According to CAN/CSA-S16, I-sections subject to flexure are classified into four classes depending on the width-to-thickness ratios of the web and the flanges. Compact sections of Class 1 and Class 2 can develop the full plastic moment of the cross-section while Class 3 sections are guaranteed only to develop the cross-section yield moment. Failure of Class 4 sections is controlled by local buckling: these sections fail before reaching the yield moment. A numerical investigation is performed to investigate the effect of bonding CFRP strips to the webs of I -section steel beams on the beam’s flexural strength. The main advantage of this innovative technique is delaying the local buckling of the beam’s web and allowing a slender I-section to reach its yield or plastic flexural capacity. Different details for bonding the CRPR strips to the web are investigated. The study reveals that bonding the CFRP strips to the web of a slender I-section significantly increases the critical load and may allow the beam to reach its yield or plastic capacity.

A 2D Finite Element Model of the Interventricular Septum Under Normal and Abnormal Loading

Abstract The interventricular septum is the structure that separates the left and right ventricles of the heart. Under normal loading conditions, it is concave to the left ventricle, but under abnormal loading the septum flattens and occasionally inverts. In the past, the septum has frequently been modelled as integral to the left ventricle with the effects of pressure from the right ventricle being ignored. Under abnormal loading, the septum has been described as behaving equivalent to a “flapping sail”. There has been no consideration of structural behaviour under these conditions. A 2-D plane stress FE model of the septum was used to investigate the difference in structural behaviour of the septum during diastole between normal and abnormal loading. The biaxial stress patterns that develop are distinctively disparate. Under normal loading, the septum behaves much like a thick-walled cylinder subject to internal and external pressure, with the resulting stresses being circumferential tension and radial compression, both varying with radius. These stresses are very low throughout most of diastole. However, under abnormal loading, the septum behaves in an arch-like fashion, with high compressive stresses almost circumferential in direction, combined with radial compression. We conclude that right ventricular pressures cause bending effects in the wall of the heart, and that under abnormal loading, the compressive stresses that develop in the septum may lead to an understanding of certain, previously unexplained, pathological conditions.

Interfacial debonding failure for reinforced concrete beams strengthened with carbon-fibre-reinforced polymer strips

Rehabilitation of structures using fibre-reinforced polymers (FRPs) has become a preferred strengthening technique. Crack-induced debonding failure has been repeatedly recorded when using fibre-reinforced polymer (FRP) laminates to strengthen reinforced concrete (RC) beams and (or) slabs in flexure. A testing programme has been performed to determine the effect of the concrete compressive strength and the amount of shear reinforcement on the interfacial debonding. The ultimate strain at failure in the bonded laminates (usage efficiency) and the strain compatibility between the laminates and the concrete sections have been investigated. The current design methods for reinforced concrete members strengthened with FRP do not explicitly consider the interfacial debonding failure; using the results of the experimental programme, the applicability and limitations of these design methods are identified. New design procedures are proposed and compared with the experimental programme results and the currently adop...

Concrete Gravity Dams: Coupled Thermal-Stress Numerical Analysis

Summary During the process of setting-out and hardening in concrete, the temperature profile shows a gradual nonlinear distribution due to the development of heat of hydration of cement. At early ages of concrete structures, this non-linear distribution can have an influence on crack evolution, especially in mass concrete such as that used in concrete gravity dams. It is thus important to study the factors affecting the amount of heat generated in the hydration process and minimize it as much as possible in order to prevent the generation of undesired cracks through the dam’s body. Coupled thermalstress finite element analysis has been performed on a full-scale concrete gravity dam to determine the impact of changing the time intervals in concrete placing schedule on the thermal/stress response of the dam. The significance of time, material and environmental factors has been scrutinized in this numerical investigation. The investigated parameters are the construction schedule of casting concrete, the cement content and the ambient temperature. The investigation also numerically explored the effect of water pipe cooling of mass concrete on the generated temperature and induced stress in concrete which ends up with recommending the most effective strategy for pipe cooling.