Análisis de las redes de apoyo y protección a la mujer

Further research in applying LPT to concrete beams can include preparing and testing full- scale continuous concrete beams, or even large scale roof systems including LPT in the main beams. Such type of testing will not only help understand more LPT, but also will highlight the effect of LPT when applied to a continuous beam in different locations (above support and at mid-span simultaneously). It would be reasonable to assume that, in this case, jacking forces F (having opposite directions), will create a couple that counters the bending moment from loading and therefore, further delay the cracking of the beam. Also, testing roof systems (for example, these systems will use cast-in-situ main beams with LPT and precast concrete ribs for the perpendicular direction with a cast-in-situ top concrete slab) will help better understand the overall effect of post-tensioning on moments redistribution in perpendicular directions.

LPT can be used in new composite steel reinforced concrete roof systems. These systems use steel I-beams as a main tensile element, with concrete cast-in-situ concrete slabs (connected to the steel beams with shear studs) as the main compressive element. LPT can be adopted at mid-span in a similar way to that explored in Chapter 6 in the lower section of

118 the steel beam (both internal and external LPT can be used, however the internal type is more aesthetical when the beam is located inside a building). In the above support area, LPT can be applied externally to the steel beam’s top flange before casting the concrete (the bars therefore will be completely embedded in the concrete slab). Such arrangement will significantly increase the overall load-carrying capacity of continuous composite beams and increase the crack resistance of the concrete slab in the above support area, allowing for significant savings in height for multistorey buildings due to reductions in overall ceiling depth.

Additional research can also be done in the area of post-tensioned timber. All panels tested in this study had the same post-tensioning configuration, where a 0.8 mm thick bracing strap was used to implement the LPT. More hogging deflections can be achieved by using thicker straps (1 or 1.2 mm) that allow more tensile force in the bottom section of the panel in an analogous way to that used in strengthenign and upgrading steel beams (Chapters 5 and 6), where increasing the diameter of tensioning rods (reinforcing bars) resulted in an increase of the tensioning force and therefore the level of post-tensioning, however, that may or may not further affect the dynamic response of the panels, therefore further research in this direction is required.

LPT can be adopted for low-grade timber panels. Previous research at UTAS and CSAW showed that control of deflections in low-grade timber can be enhanced by attaching a soffit that acts as a tensile element (Section 2.2). As an alternative, LPT can be used to create initial hogging deflections in these panels and allow them to be used in residential construction. Further testing is required to fully understand the behaviour of such panels.

119 As for the application of LPT to existing structure, it is recommended to investigate the behaviour of repaired steel beams using LPT under cyclic loading, since the majority of damaged steel beams are located in bridge structures. It is worth mentioning that the researchers already performed a preliminary testing in this area (results were not included in this thesis). Three steel beams were strengthened using LPT and tested under cycling loading. Test results showed absolutely no failure even after 2 million cycles of loadings, which by far, exceeds all cyclic testing results for repaired steel beams, obtained using other strengthening techniques (CFRP and welding in particular). This is mainly due to the geometrical setup of LPT, where the internal force in the bar, N, restricts any opening of the crack under loading. However, further investigation is required to fully understand the behaviour of LPT under cyclic loadings.

Further research in this area could also include repair methods incorporating both LPT and CFRP. The CFRP in this case will contribute to the overall load-carrying capacity of the beam, while the LPT will prevent the delamination of CFRP under static or cyclic loadings as well as increase the stiffness and load-carrying capacity of the beam).

Finally, external LPT, where the rebars are fixed to the beam’s flange could be also used to repair and restore the load-carrying capacity of steel beams (external LPT was implemented for upgrading steel beams, see Chapter 6).

In this part of the study, no bracing or other restrictions preventing buckling of the compressed beam flange were used in this study. Further testing in this direction is needed to study the effect of the boundary restrictions on the behaviour of the locally post- tensioned beams. This is relevant in particular to beams strengthened using LPT.

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Appendices

Appendix 1. Configuration of the data acquisition system used in Chapters 3