LVL Beam Problem

[ken]

by ken » Sun Aug 13, 2006 10:28 am

**LVL Beam Problem
**8/13/06

LVL (MircoLam) beam is commonly used in the residential construction.
Sometimes, we need to use it to support a floor framing and also use a steel post to support the beam.
What are the support framing details like?
If the connection details are not well designed, you will encounter some field problems. (see photos taken for an apartment building floor framing)

-Multiple LVL beam connection details
-Beam bearing
-Beam to column connection
-How to fix the problems?
-Others (?)

[ken]

by Bruce Pooley » Tue Aug 15, 2006 7:50 pm

The bottom photo shows one of the major problems with the LVL to an adjustable steel post, that is lateral stability of the beam.

The connection as shown allows a hinge to form at the location where the LVL bears on the wood plate. This hinge allows the bottom of the LVL to move laterally with the top of the post. The top of the post is not restrained either and under certain conditions can move laterally.

One solution is to use wood framing from both sides of the beam to brace the bottom of beam to prevent the lateral movement. Sometimes a metal strap is used by connecting to the floor framing to the bottom of the beam and then to the framing on the other side of the beam.

This also happens when steel beams are supported on steel posts in residential construction. It happened in my home and the EOR made the builder install wood diagonal braces.

Anyone have other solutions?

[ken]

by ken » Wed Aug 16, 2006 4:50 pm

Well described on the behavior of a wood beam under load.

The "hinged" bearing point caused a lateral beam deflection resulting the offset of the load bearing point condition.

The LVL beam basically is lacking a "kicker" like bracing system, at both sides of the beam centerline, to restrain the beam "top" flange from rotation. (Similar to the unbraced concept in designing the steel beam)

The suggestion to prevent this kind of problem will be:

-Ensure load bearing is uniform from floor framing to beam.
-Add 2x6 kickers at a proper spacing (ex. 3'-0" to 6'-0" o.c.) for lateral constraint.
-Adjust the column height properly to provide a continuous load bearing support.
-Provide adequate nailings between subfloor plywood and LVL beam.
(add glue to position the nail patterns)
-Field check the beam alignment along the bearing point (i.e. column location)
-Design footing pads properly

-Ken