ASDIP CONCRETE is a structural engineering software for design of concrete members. It includes the design of concrete or masonry bearing walls subject to gravity loads and out-of-plane wind pressures, based on the latest ACI 318 and TMS 402 provisions.
The design of masonry walls involves the calculation of shears and moments for the factored load combinations, and then the calculation of the slenderness effects to finally design the reinforcement accordingly. But what happens if the wall is not completely solid, but it has a door or window opening? This document shows an example of a wall opening design using ASDIP CONCRETE.
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Wall opening design example
As an example, consider the masonry wall shown below, which is part of the enclosure of a one-story commercial building. The roof height is 16'-0" and there is a 3'-0" parapet. Most of the enclosure is solid, but in one location there is a 12' x 8' window opening. The wall is exposed to dead, roof live, and wind loads. Design the required reinforcement for the wall opening.
How do you reinforce the wall opening?
A lintel beam is required at the top of the opening in order to support the portion of wall above. Based on the geometric information, ASDIP CONCRETE determines whether to consider the arching effect in the lintel design, and calculates the tributary gravity loads accordingly. In addition, the lintel will be exposed to a lateral pressure due to the tributary area to the lintel. In this example the window frame will transfer the lateral pressure at top and bottom of the opening, so one half of the pressure on the window will be resisted by the lintel.
A sill member is required at the bottom of the opening in order to resist the lateral pressure on the portion of the wall below, as well as the lower half of the window. Since the wall supports the sill, no design for vertical loads is required.
The lateral reactions of the lintel and sill are applied to the jambs as concentrated loads. The jambs then must be designed as vertical beams to resist the tributary portion of the wind pressure plus the concentrated reactions of the lintel and sill. The jambs in turn will transfer the reactions to the diaphragms above and below the opening.
The image below shows the ASDIP CONCRETE user interface to specify the sizes and reinforcement of the members described above. Note that the lateral pressure on the opening can be distributed in three different ways. Usually the jambs are formed of block cells specially reinforced, as in this example, but they can also be designed as concrete members.
How do you design the lintel, sill, and jambs?
With the loads described above, the software calculates the maximum moments and shears at each reinforcing element and compares them versus the structural strengths. If the lintel is precast, then the calculated load should be used to select the required lintel size in the load tables by the manufacturer.
ASDIP CONCRETE includes a section in the Condensed and Detailed tabs and reports, with the calculations of lintels and jambs for the controlling load combination. The screen shot below corresponds to the Condensed report of this wall opening design example.
Frequently the exterior walls contain openings for doors and windows. ASDIP CONCRETE has a module for the design of such bearing walls with openings, which includes the design of reinforcing members such as lintels and jambs.
For engineering background, see the post Bearing Walls Under Out-of-Plane Loads: A Design Overview. For the user interface of wall opening design, see the post CMU Wall Opening Design – New Feature in ASDIP CONCRETE. For our collection of blog posts about concrete design please visit Structural Concrete Design.
Javier Encinas, PE
ASDIP Structural Software