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Title:	Elastomeric polymers for strengthening application of concrete structures subjected to dynamic effects
Authors:	H. M. Chandima Chathuranga Somarathna (P73101)
Supervisor:	Sudharshan N. Raman, Dr.
Keywords:	Polyurethane elastomers Elastomers Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia
Issue Date:	26-May-2017
Description:	Most existing reinforced concrete (RC) structures are designed and constructed using medium range normal strength concrete, and are vulnerable to dynamic loadings including high impulsive loadings. This research was formulated to study the behaviour of palm oil based polyurethane (PU) as a strengthening material to enhance the dynamic structural capacity of concrete structures. An investigation on the behaviour and the morphology of eight types of PU elastomers was undertaken to characterise their physical, mechanical, chemical and thermal properties under quasi-static conditions. Subsequently, the uniaxial tensile characteristics under loading and unloading conditions, and the cyclic softening behaviour of selected four types of PUs were examined under varying strain rate regimes. Based on the findings of the experiments, a viscoelastic constitutive model was proposed to model the mechanical properties of the material. In addition, hyper-viscoelastic constitutive models were also developed by modifying existing hyper-elastic models with existing viscoelastic models and the proposed viscoelastic model, and were verified through the experimental results. The effectiveness of PU coatings to enhance the mechanical response was analysed using scaled concrete samples by conducting flexural tests under different strain rates. The variable nature of the proposed technique was assessed, and the influence of the thickness, position and location of coating were evaluated with 15 different coating configurations. The bonding strength of PU and concrete, and effect of slipping rate on the bonding characteristics were also experimentally investigated. Subsequently, finite element (FE) analysis were performed using the explicit solver of FE code, LS-DYNA, and were verified using the experimental findings. Parametric studies were undertaken to evaluate the main parameters that contribute towards the overall effectiveness of the proposed technique. The experimental findings under quasi-static condition suggest that the palm-based PU contributes positively both in terms of energy absorption and dissipation, and load dispersion mechanism. The findings under dynamic condition showed that the stress-strain behaviour of all PU were non-linear, rate dependent, and inelastic/plastic and that it exhibits hysteresis and cyclic softening. The proposed viscoelastic model showed the best representation, and the proposed hyper-viscoelastic models can be used to predict the material behaviour using only one set of hyper-elastic model parameters at a certain strain rate. Experimental findings of the dynamic response of scaled concrete samples showed that the dynamic resistance of the specimen correlates directly to the coating thickness, and just a 5% thick coating enhances the strain capacity by 3.3-4.6 times, strain energy density by 3.6-5.1 times, with marginal enhancement in the ultimate stress when coating is applied on either side. Meanwhile, findings of the FE analysis showed that the PU coatings reduced the maximum displacement and support rotation significantly when the structure is subjected to blast loadings. Coating on the rear face provided a high level of protection compared with coating on the impact face. The effectiveness offered by the strengthening application was also more pronounced at lower blast level scaled distances, which represent high blast intensity. The overall findings of the research showed that the mass concentration of PU on the impact face enhances the dynamic resistance of concrete elements by increasing strain and energy absorption capacities. By contrast, mass concentration on the rear face has no significant influence.,"Certification of Masters/Doctoral Thesis" is not available,Ph.D.
Pages:	303
Call Number:	TP1180.P8S596 2017 3 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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