Papers by Keyword: Strengthening

Abstract: FRP strength technique can increase the lateral strength of masonry walls, but the effect of the presence of pre-damage in the walls before retrofitted has not been studied. In this study, the experimental results from two half-scale RC-brick masonry walls with opening retrofitted with BFRP composite strips are presented. One wall was initially damaged in shear loading up to its maximum strength, and then repaired with BFRP sheets; another one was directly strengthened with BFRP sheets in the same strengthening configuration. All the walls were subjected to cyclic in-plane shear loading up to failure. Compared to the strengthened walls, the repaired masonry wall has almost the same failure mode and FRP strain rule, and slightly lower lateral strength and deformation capacity as well as energy dissipation capacity.

Abstract: The purpose of this study is to investigate shear performance of RC beams strengthened with combined CFRP and steel plates. Fourteen beams were tested to shear failure under simply supported four-point loading conditions. The variables of this investigation included strengthening technique, shear span to depth ratio, percentage of CFRP, percentage of steel plate, CFRP and steel plate orientation, CFRP and steel plate wrapping type. The results show that the simultaneous application of CFRP sheets and steel plate greatly increases the shear resistance of RC beams. The steel plates improve the bond behavior of CFRP sheets. A design formula is proposed to calculate the shear resistance of the beams strengthened with combined CFRP sheets and steel plates. The predictions agree well with the test results.

Abstract: To protect Chinese ancient buildings, tou-kung (bracket sets) in the Forbidden City in Beijing were taken as example to study their aseismic constitution problems and strengthening methods by survey as well as analysis methods. According to constitution characters and mechanical performances of these tou-kungs, their typical aseismic constitution problems were summed up, causes for the problems were discussed, and strengthening advices were proposed. Results show that typical aseismic constitution problems of these tou-kungs include decay, crack, deflection, slack and disengage of parts and so on; main causes relate not only to constitution, construction and bearing performances of bracket sets, but also material properties of wood; besides, effectively strengthening methods for these tou-kungs include reassembling, gluing, iron components connection and so on.

Abstract: In the modern building construction, different size of openings are provided in the web of reinforced concrete (RC) deep beams to accommodate utility pipes and ducts of essential services such as electricity cable, telephone network and air-conditioning network. However, accommodation of such openings caused reduction in beam strength, stiffness and caused excessive cracking and deflection. Many investigations were conducted to study the behaviour of openings in beams and relevant strengthening options to reinstate the lost capacity. One of the strengthening options considered lamination of fiber reinforced polymer (FRP) sheets due to its superior properties such as high tensile strength and stiffness, high resistance to corrosion, excellent fatigue performance and good resistance to chemical attack. FRP lamination has been widely accepted by the research community and practicing engineers in the construction industry as the material for strengthening and rehabilitation of common problems. However, quite limited literatures contained the use of FRP to strengthen RC deep beams with openings. This paper discussed the review of eleven different articles contained study of RC deep beams with openings together with effects of strengthening using FRP sheets. The outcome of this review paper outlined the way forward and future research focus in this area.

Abstract: Externally Bonded (EB) composite materials are becoming a widespread solution for strengthening interventions on masonry buildings, even Cultural Heritage structures, due to several positive aspects mainly related to their high strength-to-weight ratio. In recent years, beside common epoxy-based Fibre-Reinforced Polymers (FRP), steel-based composites have been proposed: they are composed by unidirectional high-strength steel cords that can be coupled to either organic (Steel Reinforced Polymers, SRP) or inorganic (Steel Reinforced Grouts, SRG) matrices, in relation to their optimized spacing. The bond behaviour of all these EB composites has a strong influence over the effectiveness of interventions, since the detachment of reinforcements from the substrate generally represents the weaker failure mechanism. In order to improve this aspect, several anchorage devices have been proposed, being spikes, among them, one of the most suitable for masonry supports. Spikes are made of a bundle of fibres partly in the form of a bar, to be inserted and glued into a hole drilled in the substrate, and partly loose, to be spread and connected to reinforcement strips. Despite their importance also from a design point of view and considering the variety of shapes and materials, there are still few investigations in this field, being clear that both the spike-to-reinforcement and the spike-to-masonry connections need to be studied. Focused on the spike-to-masonry connection, this paper is aimed at investigating the performance of steel cord spikes applied to existing clay brick masonry, by means of overall 39 pull-out tests carried out taking into account the bonded length (equal to the hole depth), the type of embedding material and the number of steel cords forming the anchorage. The main results of this experimentation are herein presented and discussed.

Abstract: Compared to more traditional techniques, the application of Externally Bonded-Fibre Reinforced Polymers (EB-FRP) represents a viable alternative for the strengthening of masonry structures, also in case of Cultural Heritage buildings where strict requirements need to be met, aimed at minimizing the impact of the intervention. Since the FRP-to-masonry bond behaviour strongly affects design and effectiveness of such interventions, several investigations have been carried out in recent years to study this phenomenon, generally based on the longer experience developed for concrete substrates. Mortar joints, which are geometrical and mechanical discontinuities, distinguish and characterize masonry substrates from concrete ones, and therefore deserve a special attention as far as their role in the bond behaviour is not clarified yet. This paper, aimed at giving a contribution also from a methodological point of view, presents the main experimental results of shear tests carried out on glass composites (GFRP) applied to natural calcareous stones (pietra leccese), to lime mortar blocks and to masonry prisms made by coupling stones and lime mortar. Overall 22 shear tests were performed, keeping a bonded length of 200 mm for stones and mortar specimens while it was changed from 65 mm (corresponding to one stone and one mortar joint) to 195 mm (three stones and three mortar joints) in the case of masonry prisms. The effect of the FRP end anchorage on the test development was investigated as well, and results of the experimental tests are herein discussed in detail.

Abstract: In recent decades, the construction industry has witnessed a rapid growth of interest in strengthening and retrofitting of existing reinforced concrete (RC) and masonry structures. Fiber reinforced polymer (FRP) composites have gained great popularity, and several studies are now available in the literature on their use in strengthening and retrofit applications. Promising newly-developed composite materials are represented by the so-called fiber reinforced cementitious matrix (FRCM) composites. FRCM composites are comprised of high strength fibers embedded within a cementitious matrix that is responsible for the stress transfer between the existing structure and the strengthening material. FRCM composites are still in their infancy, and very limited results are available in the literature on RC and masonry strengthening applications. This study presents an experimental campaign conducted on different FRCM composites comprised of glass, carbon, or steel fibers embedded within two different cementitious matrices and applied to concrete prisms. The single-lap direct-shear test was used to study the stress-transfer mechanism between the FRCM composite and the concrete substrate. Two different composite bonded lengths were investigated. Debonding occurred at the matrix-fiber interface for some of the composites tested and at the concrete-matrix interface for others. This work contributes to the study of the bond behavior of FRCM composites, which represents a key issue for the effectiveness of FRCM composite strengthening.

Abstract: The paper presents a structural analysis, restoration programme and scope of conservation work essential for protecting historical values based on the example of an overstretched retaining wall providing support for the embankment of an heritage church. The focus was on analysing the status of an historic stone wall constructed in part with bog iron ore (metal ore or iron-rich sedimentary rock). Ore was used for iron smelting and also as a building material. Bog iron ore was frequently used in construction across Poland, especially in places where the raw material was locally available, aesthetically attractive and had mechanical properties approximating the durability of ceramic bricks. The material was characterised by high porosity, low resistance to diffusion and high resistance to freezing, which meant that it could be used successfully in structures subjected to atmospheric impacts without additional protection

Abstract: In this paper we present the study of an archaeological structure in Pompeii and we detail the difficulties encountered applying the Italian standards and guideline when designing the new roofing structure. Following the latest Italian standards and guidelines, about the assessment and mitigation of seismic risk of cultural heritage, the analysis of the Insula has been carried out. In particular, among all the studied structures, the attention was focused on the covering of the main hall where a prototype of a roofing structure covering a portion of the hall was installed near the remaining ruins of the house. Numerical models have been developed in order to track the effect of these new roofing structures on this ancient masonry structure.

Abstract: A FE beam model to perform static and dynamic analysis of fiber-reinforced masonry arches is presented. Based on a constitutive equation formulated for no-tension masonry beams, the model accounts for a limit to the material deformability and provides for irreversible damage occurring under compression. In order to capture any possible FRP debonding, a procedure is also formulated to reduce the performance of the fiber when the tangential and normal stresses at the masonry-composite interface reach a critical value. Some dynamic analyses are performed on a case study with the aim of evaluating the effectiveness of FRP-retrofitting in improving seismic performances.