RAM | STAAD | ADINA Wiki Design Strips and Slab Openings [TN]

Design Strips and Slab Openings [TN]

	Applies To
	Product(s):	RAM Concept
	Version(s):	Various
	Area:	Modeling; Analysis; Design

Overview

The purpose of this tech note it to aid users in defining design strips and understanding the layout of program reinforcement around slab openings.

Design Strips and Slab Openings

The layout of span segments and generated design strips will depend on the size of the slab opening and its location relative to the column grid line.

In general, it is best to model span segments so that they do not pass through a slab opening. When slab openings occur on a column grid line, the span segment may be shifted to one side of the opening or it may be divided into segments on each side of the opening.

Small openings often lie between cross sections. These openings affect the design forces determined from the finite element analysis; however, the cross sections in the design strip are the same as those in the same design strip without the opening. In other words, the opening has no effect on the cross sectional areas used in the design checks. For these openings, the design strip hatch will extend through the opening and the extents of the program reinforcement will extend through the opening. See Figure 1.

Figure 1. Small Opening Example

Most openings intersect a cross section. When this occurs, the opening reduces the area of the cross section causing some cross section to be narrower than other cross sections. The boundary of the design strip is drawn as a series of line segments between the ends of adjacent cross sections so that the hatched design strip excludes much of the opening and the boundary of the design strip is skewed. In this case, the non-uniform design strip boundary can be ignored because it acts as a marker, enveloping the different cross sections widths in the design strip. For these openings, the program typically places bars only in the narrow width without distributing the bars into the extra width in the wider cross sections on either side of the opening. See Figure 2. When the layout of program reinforcement is unacceptable, user reinforcement may be used to override the program designed reinforcement.

Figure 2. Large Opening Example

The layout of program reinforcement may be improved by modifying the layout of the span segments. For example, the design strip may be divided into cantilever strips that run from column to edge of slab with narrower strips on either side of the opening (See Figure 3 and Figure 4).