Building Management Hawaii February/March - (Page 31)

Ask an Expert No One Likes to Sag Few things are more worrisome than seeing your lanai loll. By Jon Brandt Recently I was asked to look at a building where the owners were concerned that their lanai were starting to fall off the building. They were the typical concrete lanai that cantilevered off the side of the building, the kind so common on buildings here. And the building was older so they thought it best to call an engineer since they started seeing new sagging on the lanai. The lower level lanai showed the most damage, and as I looked higher the damage got less and less. I also noticed that most of the sagging lanai had been enclosed, and the unenclosed lanai showed no damage. So I started to ask about the enclosures, but the owners said that the lanai had been enclosed a number of years ago and assured me that they couldn’t be the problem. Well, actually they were the problem. When the lanai were enclosed, the contractor installed very wide and stiff aluminum sections to support the new windows. These supports started to act like columns connecting the upper lanai together. As owners started to use their new enclosed lanai for storage, the additional weight caused the lanai to want to sag. This normally wouldn’t have even been noticed, but because of the aluminum sections, the lanai couldn’t sag and the weight was transferred to the lower lanai. At a certain point, the lower lanai couldn’t take the strain anymore and started to sag a lot and caused damage to the building. I’ve seen similar situations, but usually the aluminum sections are a lot smaller and they buckle under the weight. I’m sure the window installer was proud of his work, thinking the large aluminum sections would provide a lasting window system, but it only led to damaged lanai. Although the windows had been installed years ago, concrete can take years to deflect (or sag). All materials deflect when additional weight is placed on them. Sometimes the weight is small compared to the beam supporting it so the deflection isn’t noticeable, but it’s there. And all the deflection doesn’t happen right away either. Materials such as steel and wood have most of their deflection as soon as the extra weight is placed on them, but then over time a small amount of extra deflection occurs. On the other hand, concrete can have the majority of deflection occur over a long period of time with very little deflection right away. There is actually a building code requirement for this. Engineers are to consider the deflection of the concrete beams after five years of service. That doesn’t mean that the deflection is complete at five years, but shows that it is an issue. On this project, the owners will have to rework those windows and repair the damage, but the concrete is fine. Sometimes the continued deflection of concrete does indicate a bigger problem. If your building has similar issues be sure to have it checked by a local licensed structural engineer. Jonathan Brandt, S. E., is the principal of JPB Engineering, Inc. and has engineering licenses in Hawaii, California and Guam. He has worked in both the construction and engineering fields and has more than 10 years of engineering experience. Visit BMH February–March 2013 31

Table of Contents for the Digital Edition of Building Management Hawaii February/March

Top 3 Energy Incentives
On The Grid
Solar: Not A Singular Solution
Saving Money & Art
Payback Projects
Top 10: Turn Energy Into Value
AC: Light-Zapping Clean
Does Your HVAC Talk BACnet?
Editorial: Industry Insights
Association Updates & Industry News
Ask An Expert: No One Likes To Sag

Building Management Hawaii February/March