Phd thesis concrete slabs

It is generally advantageous to introduce an explicit hierarchy of work activities for the purpose of simplifying the presentation and development of a schedule. For example, the initial plan might define a single activity associated with "site clearance." Later, this single activity might be sub-divided into "re-locating utilities," "removing vegetation," "grading", etc. However, these activities could continue to be identified as sub-activities under the general activity of "site clearance." This hierarchical structure also facilitates the preparation of summary charts and reports in which detailed operations are combined into aggregate or "super"-activities.

Tightening of the prestressing cables of 30-cm mass concrete slabs, bridging an 11-m enlargement. Valencian Institute of Modern Art (IVAM), Valencia.
SOURCE: [1] A waffle slab with 40-cm-high system formwork, edge of (40+ 5) cm or (40 +10) cm, and prestressed ribs with two non-adhering stranded wires of or inches, could allow spans of 15 to 20 m, while simultaneously minimising the problem of deformations. It suffices for the deviation forces to oppose each other and cancel out the loads of the own weight to assure a horizontal mass concrete slab with zero deflection.

In addition, compressive prestressing reduces and cancels out rheological cracking in the slab (map cracking, shrinkages, etc.), which is so difficult to avoid in traditional reinforced concrete slabs.

After this brief introduction to waffle slabs through their main parameters, the following examines slab deformations, owing to their direct relation to the installation of direct adhered modular rigid flooring.

In the case of waffle slabs, the quantitative evaluation of deflections from formulas or mathematical models is even more complex, perhaps even unencompassable, because of the problems stemming from torsional mechanisms, the difficulty of quantifying these in waffle slabs, and the high degree of cracking that usually occurs in the compression layer.

The model of finite elements [PhD thesis of Luis García Dutari] and the model of virtual gantries, based on the concept of Effective Inertia [by . Branson] and adopted in Instruction EHE , as well as theoretical calculation models such as the CYPECAD software [1] , provide a qualitative approximation for foreseeing deformations.

Just as in beam and pot floors, this involves an approximation to waffle slab deformation, taking into account the following:

  • The directives and requirements established by the instructions and standards. In the case of Spain, the Instruction on Structural Concrete EHE
  • The quality of the materials (concrete and steel)
  • Structural dimensioning in project designs and the most recent advances
  • The influence of envelopes and partition walls
  • Integral management of the deformations, from the approaches in the design phase to the actual construction process, including the ‘impositions’ of the Developer
All these points are the direct responsibility and competence of the Designer and the Specifications writer, which is why these fundamental aspects in the consideration of deformations are not further dealt with here. The Reader is urged to consult the contents on the subject matter offered by Florentino Regalado in chapter 10 [pages 341-413] of his Treatise on waffle slabs [1] , particularly the section on integral deformation management [pages 409-413], which sets out certain fundamentals on this issue.

Among the different documentary sources available, with a view to approximately assessing the magnitude of deformations in waffle slabs, mainly as a function of the span, edge, and column size, the example given in section of source [1] has been set out (Analysis of the variations displayed by vertical strains of the centre points of the basic boxes of a waffle slab, as a function of the spans, edges, and column sizes).

Phd thesis concrete slabs

phd thesis concrete slabs


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