Development and assessment of ultra-high performance fibre-reinforced composite panels

Abstract

Ultra-high performance concrete (UHPC) is a newly-developed and advanced cementitious material which provides superior strength, durability, and life-span in comparison to conventional concrete. However, under tension it is susceptible to large cracking followed by brittle failure, and this is undesirable in flexural members and frame systems. This is minimised with the addition of steel fibres, resulting in the development of ultra-high performance fibre-reinforced concrete (UHPFRC). UHPFRC provides superior tensile strength and strain hardening properties, and the inclusion of steel fibres provides additional ductility in the post-cracking region, a desirable mechanical property in the design of composite slabs and panels. This thesis presents a collection of journal articles outlining the development and structural assessment of various UHPFRC composite panels jointly with a range of regular and advanced materials. In the first section of this thesis, the bubble deck and box girder structure systems are used to conceptualise, develop, and produce two new forms of ultra-high performance concrete (UHPC) and ultra-high performance fibre-reinforced concrete (UHPFRC) composite panels for which their structural performance is investigated. An experimental program is performed to observe the one-way bending behaviour of sandwich and box-celled panel systems, and analytical and numerical solutions are established to predict the panel behaviour at the serviceability and ultimate limit states. The section highlights the effectiveness of both systems as viable in structural engineering applications and in particular, the ductility of the box-celled panel. The second section of the thesis focuses on investigating the feasibility of the box-celled panel system as a wind-resistant structural element. Panels implementing helically ribbed glass fibre-reinforced polymer (GFRP) and steel reinforcement are produced and tested under three-point flexure in both directions to understand the full-range flexural behaviour of the system. The panels display high load capacity and ductility and their behaviour dependent on the reinforcement detail, with GFRP reinforced specimens exhibiting the largest flexural capacity. The results are used to assess the proposed system for compliance with current code provisions for both combined loading actions and permissible deflections when considered a main wind force resisting system (MWFRS). The panels are shown to be efficient as a MWFRS, with load and deflection criteria lying within the elastic region for both flexure directions. Having observed the reinforcement to be influential on the structural performance of the composite panels, an experimental program is performed to evaluate its bond-slip behaviour within UHPFRC. The behaviour of the helically ribbed GFRP and steel reinforcement embedded in UHPFRC is observed experimentally for various cover conditions and then used in conjunction with existing bond-slip models to develop a multi-variable bond-slip relationship. The results are compared to the steel reinforcement followed by a parametric study to observe the model variation for its key variables. The final section of the thesis concentrates on the experimental study of curved and skewed UHPFRC slab systems accompanied by analytical and numerical modelling procedures. Asymmetric and curved slab specimens are cast at various skew and curvature angles and tested under statically indeterminate conditions. Closed-form solutions are developed to predict deflections at the ultimate state, and a thorough finite-element analysis is performed to observe the full-range structural performance. A parametric study is performed to examine the variation of deflection, shear, bending and torsion along the slab length for varying skew and curvature angles. In the section, it is shown that the models can be successfully applied to predict the behaviour UHPFRC asymmetrically skewed and curved slabs.