Bond Beam 1

[NADOR123]

Hi everyone,

During the construction of a one story building a conflict on the architectical plans has been discovered between the doors and louvers lintel elevation and bond beam elevation.

The contractor wants to stop the bond beam where it meets the lintels and add a small bond beam above the lintel level rather than add another course and build a continuous bond beam above the lintel course.

My argument is that the bond beam must be continuous throughout the perimeter of the building but the project architect thinks that the contractor proposal is acceptable.

Any ideas if there is a back up supports that bond beam must be contentious.

Thank you

 

[ToadJones]

Can you use a concrete lintel?

 

[rlflower]

Requesting clarification: wall construction type?

Richard L. Flower, P. E., LEED Green Associate

 

[concretemasonry]

It sounds like a CMU construction and the contractor and/or architect want a control joint at about the edge of one side of an opening for crack control. This is very common.

The main function of the bond beam at the top of the wall is to provide a solid masonry element to distribute any added point loads into the classic distribution pattern for masonry construction.

Usually, the bond beam does not pass through a control joint unless it is permitted to have a slip joint (greased end) to allow longitudinal movement, but not allow vertical or out-of plane wall movement. This allows the necessary movement and control where the movement will be so there are no random shrinkage or temperature cracks. T%he location of the control joint above and below the opening should be determined by the designer to maintain aesthetics.

I am basing this on my assumption of the building construction assumption and some standard practice. I could be wrong if the wall in not CMU single wythe or a block/brick cavity wall.

Dick

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hokie66]

Why can't the bond beam and lintel be the same member? If it needs more reinforcement over the opening, just provide it.

 

[concretemasonry]

They definitely can be the same unit. I did that on my lake home. I used a 16" deep block lintel (horse collar) over the 4 - 6' sliding door assembly, but still put a control joint in the brick at each end of the 4 window assembly. The bond beam steel became the top steel in the lintel and the bottom steel was cut at the end of the lintel section. The exterior control joint was only in the top courses of the brick veneer and set off the window opening edge slightly to start at the end of the CMU lintel section.

You still have to be concerned about a control joint, so the treatment of the horizontal rebar in the bond beam remains.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hokie66]

I don't like control joints at openings or lintels that have to slide. Seems better to me to place the control joints between openings. Anyway, the OP didn't say anything about control joints.

 

[rowingengineer]

I don't like control joints in CMU, but will add them under duress.

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[NADOR123]

Hi

The wall is CMU single wythe and the steel lintel at the same elevation of the bond bbeam at top of the CMU wall.

Thanks

 

[ToadJones]

I don't know why there is all this talk about control joints?

Hokie-
When I suggested a concrete lintel, my thinking was to have the bond beam and lintel one in the same.

 

[rlflower]

Please inform us of the status of the construction. Has the steel lintel and/ or the bond beam been constructed yet?

Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.

 

[NADOR123]

The building is under construction but the bond beam and the steel lintel have not been constructed yet.

 

[rlflower]

Then I concur. Make the top course of CMU a continuous bond beam (not much added cost), or construct it out of concrete.

Richard L. Flower, P. E., LEED Green Associate
Senior Structural Engineer
Complere Engineering Group, Inc.

 

[concretemasonry]

More substantial information is necessary to determine why the contractor wants to create a joint to isolate the lintels horizontally and why the architect agrees (maybe it is based on experience). Not all things done acceptable do not turn strictly on detailed structural analysis. - If this is a typical large one-story commercial or industrial building I can seen the reasons for the agreement.

1. What are the over-all building dimensions (height, width and length).

2. What is the wall panel or open wall spacing and what are the opening heights/locations relative to the wall elevation. I assume (bad word) that the louvers are higher on the wall unless there is floor ventilation/evacuation.

3. What is the wall construction? - materials, thickness, etc.

This is necessary to avoid the myopic analysis similar to the three blind men independently examining an elephant with one hand, no sight and ended up with no agreement.

Unless the building is very small there is always some provision to accept the inevitable movement. I observed a load bearing back wall of a 600' long, 12-14' high commercial/industrial building that had no provision for movement in the wall, but there were 8 man doors (7' high opening) and a continuous 16" deep bond beam/lintel with 4 -#6 bars continuous. Upon investigation, cracks were observed at one edge of each opening. After that, there were cracks at the midpoint of each remaining panel between each of the openings. After the first set of natural cracks, there was another generation of cracks to further subdivide the panels for the temperature and humidity conditions. - There was also on continuous horizontal crack immediately below the continuous bond beam/lintel. The CMUs used were very low shrinkage (less than 1/4 of that allowed for the Type I units at the time) and dry. The architects and engineer lost all further business with the very large client because of the water leakage caused by the 600' horizontal crack - During my 40 years experience in the U.S. and elsewhere, I have seen similar, but far more obvious cases of movement such as long term brick expansion on a 7 story reinforced concrete frame apartment to where the differential movement (concrete shrinkage & brick expansion)it became impossible to open windows for ventilation or emergency access.

You have to look at the big long term picture of the structure, materials and movements that can create problems reflecting back on the professional design. - If not, you may mistakenly identify and elephant for a snake like the blind man.

My comments, as I originally mentioned, were based on the information provided and the information so far really has not been sufficient for more than a quick "boilerplate" solution.

The bottom line is that you probably will not find a specific requirement on continuous steel in bond beams because of the possible detrimental visual maintenance and effects without a structural benefit. IF is is a masonry wall, the purpose of the bond beam generally is to provide a beam that provides a good bearing surface, vertical distribution of the loads into the wall below, resistance to differential movement from lateral loads and still allow horizontal movement of the wall below.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[NADOR123]

Hi

The building is 28' x 64' x 13' high. There are about 4 louvers 2'x2' located all the way at the top of the wall and thier lintels are at the same level as the bond beam.
the wall is 12" CMU.

Thanks

 

[structuralengr89]

When I have a load bearing block building with the cmu acting as shear walls I have always told the contractor to run the reinforcing in the bond beam at the bearing elevation continuous. If you figure your chord force from wind or seismic loading I don't see how you can interupt the reinforcing at the vertical expansion joints in the block.

 

[structuralengr89]

Let me get this straight:

You have a 1 story rectangular building. You have 12"cmu walls 13' high. I'm guessing you are in SDC A, B, or C. Your walls span vertically with reinforcing at some spacing and you have a single bond beam at the top of the wall- I'm guessing ladder reinforcing at 16" o.c. for horizontal S&T.

These louvers are at the top of the wall (13') and cut your continuous bond beam. If your cmu is your lat force resisting system (cmu shear walls) and this top bond beam has to handle your chord force, then you need to figure how your diaphragm load is going to get into your shear walls.