Technical Note Structural Concrete Software System

Transcription

1 Technical Note Structural Concrete Software System TN232_rebar_in_PT_slabs STRUCTURAL DETAILING FOR NON-PRESTRESSED REINFORCEMENT IN POST-TENSIONED FLOOR SYSTEMS 1 First draft October 31, 2006 Bijan Aalami 2 The non-prestressed (passive) reinforcement that is generally placed for structural detailing of post-tensioned floor systems is either for proper functioning of the post-tensioning tendons, or for improved in-service performance of the floor. This Technical Note describes the reinforcement that is generally placed for improved in-service performance. Refer to the following flow chart. It identifies three categories of non-prestressed reinforcement. (i) (ii) (iii) Reinforcement determined from analysis and design, including those specified in building codes; Reinforcement used to install and maintain tendon profiles shown on plan, such as support bars and chairs; and Reinforcement placed to mitigate cracking; complete load path 3 ; and ensure proper functioning of tendons. The focus of this Technical Note is on the third category. Figure 1 is the schematic of a posttensioned floor system with common features, such as beams, and walls. The post-tensioning tendons are not shown for clarity. Figure 2 identifies the reinforcement details for each of the floor slab features. The details of the reinforcement called out are included at the end of this Technical Note. The reinforcement called out in Fig. 2 is the minimum amount. It is not in addition to the reinforcement on the drawing from other considerations. The reinforcement in Fig. 2 supplements that shown on the drawing, if not adequate. The following is a brief description of each detail. Detail 1 Reinforcement along the edge of slab, both where supported or free Detail 2 Reinforcement at slab corners 1 Copyright ADAPT Professor Emeritius, San Francisco State University; ADAPT Principap 3 Aalami, B. O. (2005), Structural Modeling and Analysis of Concrete Floor Slabs, ACI, Concrete International, December 2005, pp support@adaptsoft.com 1733 Woodside Road, Suite 220, Redwood City, California, 94061, USA, Tel: (650) Fax (650)

2 Technical Note FIGURE 1 FLOOR PLAN ADP508 FIGURE 2 REINFORCEMENT CALL OUT 2

3 Technical Note NON-PRESTRESSED REINFORCEMENT FOR POST-TENSIONED FLOOR SYSTEMS tn232_rebar_ REINFORCEMENT REQUIREMENTS AND DETAILING Determined from analysis and design Structural Detailing Used to facilitate construction Tendon layout in-service performance of slab Mitigate in-service cracking Complete load path Avoid blow outs Anchorage detailing Set tendon profile Gravity design Lateral design Service condition Strength condition Initial condition Seismic desgin Wind design Detail 3 Reinforcement at re-entrant corners Detail 4 Reinforcement at slab corners that are supported on both sides. This reinforcement serves to address the twisting moments that are generated in such conditions. 3

4 Technical Note Detail 5 Reinforcement to mitigate cracking at slab corners that are tied to perimeter walls. This reinforcement is necessary for the first three to four levels of a tower structure, whereas reinforcement shown in detail 4 applies to all levels of a building. Moreover, detail 5 applies to where a slab edge is supported on either one or two sides, whereas detail 4 applies only where an exterior slab corner is supported on both sides. Detail 6 Distributed reinforcement transverse to beams and walls and extending over the entire length of the member. Detail 7 Reinforcement at the tip of a wall or beam Detail 8 Reinforcement along interior walls that are tied to slab. This reinforcement is generally required for the first three to four levels of a building tower. Detail 9 Reinforcement along exterior walls that are tied to slab. Again this reinforcement is generally required for the first three to four levels of a building tower. Detail 10 Reinforcement around small openings that are not included in design. Larger openings are generally modeled in the analysis and are designed for. The detail covers openings up to 3-0. Larger openings are intended to be designed for. Detail 11 Bottom reinforcement over column supports Detail 12 Reinforcement in drop caps/panels Detail 13 Stirrup to compensate for openings near and within the vicinity of critical punching shear perimeter of a column, where the presence of opening has not been accounted for in design. The stirrups are intended to compensate for the loss of strength from concrete removed by opening. Detail 14 Reinforcement in slab bands Detail 15 Reinforcement below concentrated loads. At design time, concentrated loads are oftentimes assumed smeared over the width of the design strip they fall on. The objective of the reinforcement is to insure that the concentrated load can spread over the design section assumed for its analysis and design. 4

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