SECCIÓN TRANSVERSAL PARA VÍAS EN AFIRMADO

RECOMMENDATIONS FOR FUTURE WORK

7.1. Conclusions

Several conclusions could be drawn in this study as follows:

a. A new approach to strengthened Glulam beams has been established in this research. The use of compressed wood made of a low grade wood through densification as a reinforcing material has been proved to be effective. As only a small amount of compressed wood is needed and no bonding between the CW and the beam is necessary, the techniques developed are economical and environmentally friendly.

b. The predicted pre-camber and extreme fibre strains (and therefore stresses) of all pre-stressed short beams have showed good correlation with the experimental results. For the long beams, there is good correlation on pre- camber between the simulations and the measurements for beams reinforced by three (no CW lamina), five and seven (one CW lamina) 45 mm thick CW blocks.

c. Destructive bending tests for all beams pre-stressed by the CW have also indicated that there are significant enhancements on the initial bending stiffness and the load carrying capacity. For the short Glulam beams reinforced by three 30 mm and 45 mm thick CW blocks (corresponding to the CW volume fractions of only 1.2% and 1.8%), there are increases of 19% and 22% on bending stiffness and 14% and 19% on load carrying capacity respectively. For the long beams the enhancements of the bending stiffness are 37.1% and 45.8% for the beam reinforced by five and seven CW blocks and a CW lamina respectively. In terms of load carrying capacity, a beam reinforced by five CW blocks and a CW lamina carries the maximum load of 64.3 kN, which is an 11% increase in comparison to the control beam. The beam reinforced by seven 45 mm thick CW blocks has shown a significant enhancement on the initial bending stiffness. It should

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also show a further improvement on load carrying capacity if there was no premature failure. The amount of CW used to strengthen the long beam can be increased to enhance the pre-camber and the corresponding initial extreme fibre stresses.

d. 3D non-linear finite element models have been developed to simulate the pre-camber of Glulam beams locally reinforced by compressed wood blocks. The models developed have also produced the initial tensile and compressive stresses at the top and bottom extreme fibres with building-up moisture-dependent swelling on the CW blocks. With the pre-camber and the initial stress state that cancel out proportions of working deflection and stresses, the modelling has also shown the enhancements on bending stiffness, hardening behaviour and load carrying capacity of the Glulam beam reinforced.

e. Regarding the modelling of destructive bending tests of the short beams, the predicted maximum loads are slightly higher than the test ones for beams reinforced by three CW blocks with thickness of 30 and 45 mm, and slightly lower for beams reinforced by three 15 mm thick CW blocks. However, the discrepancies are within 10%. For the long beams, all modelling results show a similar trend, with the curves demonstrating overall linear features until a certain load level, which is varied from beam to beam between 40 kN and 45 kN. The features observed after the initial yield have been simulated reasonably well.

f. Based on the simple assumptions related to the parabolic moment distribution in analytical approach, the pre-camber predicted at midspan of the short beams with various reinforcing arrangements gives a good agreement with the measured pre-camber. The assumptions related to the linear moment distribution are not appropriate for analysing the pre-camber of the beams reinforced in this way.

g. Using validated models, parametric studies have been undertaken on parameters covering the thickness, number and location of compressed

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wood blocks, as well as the depth of the opening (to accommodate the CW blocks with different heights) on the Glulam beam. The numerical data produced are useful to optimise the enhancements on pre-camber, initial bending stiffness, hardening behaviour and load carrying capacity of Glulam beams strengthened.

h. The results have clearly indicated that the reinforcing techniques developed using compressed wood blocks are very effective means to produce pre- camber, which enhances the initial bending stiffness, bending strength and load carrying capacity of Glulam beams. The technology is ready to be applied in practice.

7.2. Recommendations for future work

There are some recommendations for future work which could not be covered in this study:

a. Further experimental work in regards to creep and stress relaxation of compressed wood is needed to study long-term structural performance of Glulam beams strengthened.

b. Further numerical modelling needs to be undertaken by implementing stress relaxation law into a user-defined subroutine to investigate the tensile stress reduced on the top extreme fibre of the Glulam beam after the swelling of compressed wood and constraining of Glulam reach a balance point.

c. Further theoretical analysis needs to be carried out to predict strains (and therefore stresses) more accurately in the key locations on the strengthened beam.

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