ADAPT – Post-tensioned beam and one-way slab construction (PME0011)

OVERVIEW AND SCOPE

This report presents the structural engineering calculations of a post-tensioned floor using parallel beams and one-way slab construction. The design is based on Hong Kong building code HKCOP 2004 and its amendment of June 2007. The general criteria used for the design, such as details of material properties are given in a separate report entitled “Structural Design Criteria.” Features of the geometry and details of loads applicable to the floor slab covered by this report are included herein.

The requirements called for a “Class 3” design. This means that the computed tensile stresses at the extreme fibers are permitted to exceed 0.36√ fcu. For the specified concrete material of 65 MPa cube strength, this translates to tensile stresses exceeding 2.90 MPa. At the same time, the computed stresses shall not exceed 0.25fcu. For regions, where stresses exceed the first threshold (viewed as onset of cracking), but are below the second threshold (maximum allowable), reinforcement is added to limit the crack width to 0.2 mm.

To meet the design requirements, a low value for post-tensioning had to be specified, in order to induce cracking in the floor system.

The design moment of the slab is modified for each design section to include the twisting moment of the same section (Wood-Armer) approximation. In the general case, the design moments used for the determination of reinforcement are somewhat larger than the actual bending moments generated in the slab when the Wood-Armer approximation of the program is invoked. However, the impact for the floor system reported herein is small, since the one-way system is small.

The design uses the program ADAPT Floor Pro release 2009/2010 featuring the Hong Kong Code.

A review of the design values suggests that a more balanced design option for the subject matter floor slab would be to increase the amount of post-tensioning provided. It is noted that an undue amount of non-prestressed reinforcement is calculated and added in the design to reduce the crack width to the maximum allowable value. For the design  reported herein, the amount of non-prestressed reinforcement would be reduced substantially by a moderate increase in post-tensioning, However, the post-tensioning was kept at a low value to achieve a Class 3 design alternative.

LIST OF CONTENTS

• Structural Design Criteria for the Project – (submitted in a separate package)

Input data

o S3 Reflection of program printout of input design criteria

o S4.1 Structure plan. There may be more than one sheet. This may have to include sections, column and wall dimensions, steps, openings and possibly labels. It should give a fill definition of structure.

o S4.2 3D line drawing view of the structure

o S5 loading assumptions and calculation

o S6 Load plans

o S7 Tendon plan

Analysis and Design Values

o S15 Finite Element discretization (mesh plan)

o S20 Long-term deflection due to dead and live load

o S21 Instantaneous deflection due to live load

o S22 Support line identification is x-direction (includes label and span length)

o S23 support line identification in y- direction

o S24 design strip display in x-direction

o S25 design strip display in y-direction

o S26 Strength moment display along xx

o S27 Strength moment display along y-y

o S28 Design section stress check along xx

o S29 Design section stress check along y-y

o S30 Design Legend

o S31 Design check for each support line (there will be as many sheets as support lines)

o S32 Reinforcement plan from computations

o S40 Lower supports identification plans

o S41 Lower supports reactions

o S42-1 Punching shear stress check plan (showing stress check results)

o S42-2 Punching shear stress check tabular results

o S43-1 Punching shear reinforcement table

o S43-2 Punching shear reinforcement layout – details

o S44 Punching shear stress check parameters

ADAPT – Post-tensioned beam and one-way slab construction. Password: D$N5yn9L