Reminders from Hurricane Katrina

This week is the 10th anniversary of Hurricane Katrina, and we have all seen articles on the lessons learned from the storm. Engineers learn something new from every storm. However, I think that Hurricane Katrina just gave us some very strong reminders of things we already knew.

Hurricane Katrina reminded us that hurricanes are flood events as well as high-wind events. And I don’t mean the flooding in New Orleans. No, I mean the flooding along the Gulf Coast from Louisiana to Florida.

I witnessed the complete devastation of the Mississippi Gulf Coast from Waveland to Biloxi. Structures within the first few (and often many) blocks from the beach were simply flattened by water. Fortunately, these areas are coming back, but the structures being built there now bear little resemblance to the homes that graced the beach 10 years ago.

I remember my father-in-law having his new house built on the coast in Waveland more than 20 years ago. As a young engineer, I gave it the once over and noted that the builder had connected the roof framing to the top plate, but little else. I made some recommendations, such as continuing the connections down throughout the rest of the house to the foundation. The builder followed my suggestions and then presented my father-in-law with the bill “for your son-in-law the inspector.” He was happy to pay it. Nevertheless, although the house was wind resistant, it could not stand up to the rushing waters from Hurricane Katrina.

Katrina reminds us that the only way to get away from floods, other than not building near the water, is to elevate structures above them. Due to flood regulations, new houses along the Gulf Coast are now elevated high in the air, in the hope of avoiding flooding from future storms. Simpson Strong-Tie is proud to have developed some products during the last few years that make it easier to build structures elevated on pilings.

One such product is our CCQM column cap that strengthens the connection of support beams to masonry piers. Another is the Strong-Drive® SDWH Timber-Hex HDG structural screw, which is meant to replace through-bolts to make the connection of a beam to a wood piling easier and more reliable.

CCTQM Installation

CCTQM Installation

Elevated house built with CCQM Column Caps

Elevated house built with CCQM Column Caps

 

SDWH TIMBER-HEX HDG Screw

SDWH TIMBER-HEX HDG Screw

Hurricane Katrina reminds us of the value of building codes. After the storm, the LSU Hurricane Center conducted a number of simulation studies on the effect of a direct, Katrina-like storm on the states of Louisiana, Mississippi and Alabama. The simulations were run on the existing stock of buildings, and then run again on the same stock of buildings, assuming that certain features that result from modern building codes were present. These features included shutters or impact-resistant windows, enhanced nailing of the roof deck to the roof framing, framing connected together with hurricane clips and straps to achieve a continuous load path. In addition, in the Louisiana study, a secondary water barrier over the joints in the roof sheathing was added.

The studies found that the decrease in wind damage from the simulated storms was astounding. In Louisiana, the study showed a 79% reduction in economic losses due to wind. In Alabama, the study revealed a 72% reduction in economic losses due to wind. The Gulf states seem to have received the message loud and clear. In the years following Hurricane Katrina, Louisiana adopted a statewide building code and Mississippi adopted a uniform building code for the four counties along the coast. Recently, Alabama has also adopted a statewide residential and energy code. But in general, building codes are still quite varied in coastal states. This report from the Insurance Institute for Business and Home Safety evaluates the effectiveness of building codes in coastal states.

Finally, Hurricane Katrina reminds those of us who do damage surveys that you need to know what you are getting into before you go. As soon as the storm hit and we saw the scope of the damage, four members of the Simpson Strong-Tie Engineering Department in our McKinney, Texas, office decided we needed to go see the damage first-hand before any repairs were made. So two days after the storm struck, off we went to Jackson, Mississippi. There, we rented two vans stocked up with food, water and fuel. Unfortunately, the fuel and the food/water ended up in separate vans. Before long, we were separated in traffic and could not communicate due to loss of cell signal.

Our team spent two days viewing the damage first-hand along the Louisiana and Mississippi coast, but spent a lot of time our last day trying to find some fuel so we could make it back to Jackson. I remember spending the night in a hotel without power full of storm victims, and then months later receiving the bill and being charged for a movie!

SE Blog 4SE Blog 5

SE Blog 6

What do you remember from Hurricane Katrina? Let us know in the comments below.

Pier Decking Fasteners

This week’s post is a case study featuring a recent restoration job on the central coast of California and how Simpson Strong-Tie® hot-dipped galvanized screws proved to be a better option than traditional spikes.

A pier originally constructed in the 1800s was closed a few years ago as general deterioration caused the structure to become unsafe. As preparation for rebuilding the pier began, one of the major concerns was the attachment of the deck boards to the framing.

Traditionally, the deck boards have been attached with hot-dip galvanized 60d (0.283″ x 6″) spikes. However, spikes have a low withdrawal resistance, are typically predrilled and have a multi-step installation process. In addition, spikes, over time, can begin to back out so that the heads protrude above the top of the deck boards. This creates an unsafe condition for pedestrians and also results in ongoing maintenance work. Here you can see one of the old spikes.

Corroded spike for deck board fastening.

Corroded spike for deck board fastening.

Simpson Strong-Tie provided two options for replacing these spikes: the Strong-Drive® Timber-Hex HDG screw, SDWH27800G, and its stainless-steel counterpart, the Strong-Drive Timber-Hex SS screw, SDWH27800SS. The SDWH27800G screw measures 0.276″ x 8″ and has a hot-dip galvanized coating, conforming to ASTM A153 Class-C. The SDWH27800SS screw measures 0.276″ x 8″ and is made from Type 316 stainless steel. Both of these screws have integral washer, hex-drive heads and are self-drilling. They are not intended to be self-countersinking though, and as a result, installation with the heads below the deck surface requires a shallow dapped hole.

A comparison of the load values was provided to Shoreline Engineering, Inc. engineers Bruce S. Elster, P.E., and Jonathan T. Boynton, P.E., for their review and approval. In addition, Simpson Strong-Tie Fastening Systems/Dealer Sales Representative Darwin Waite expertly conducted on-site demonstrations for numerous decision makers including the contractor and city officials. These demonstrations allowed the contractor and owners to compare the labor costs and finished appearance of the different fastening methods.

Simpson Strong-Tie Fastening Systems Dealer Sales Representative Darwin Waite takes selfie on the completed dock.

Simpson Strong-Tie Fastening Systems Dealer Sales Representative Darwin Waite takes selfie on the completed dock.

Below is a comparison of the allowable load values* of the potential fasteners. We can see how each of the Simpson Strong-Tie screw options exceeds the spike load values in all load conditions.

Table 1. Comparative allowable properties for hot-dip galvanized spikes (60d), hot-dip galvanized screws (SDWH27600G, SDWH27800G) and stainless steel screws (SDWH27600SS and SDWH27800SS).

Table 1. Comparative allowable properties for hot-dip galvanized spikes (60d), hot-dip galvanized screws (SDWH27600G, SDWH27800G) and stainless steel screws (SDWH27600SS and SDWH27800SS).

*Not to be used for design purposes as footnotes have been left out of this blog post. Table values include wet service factor adjustments.

In the end, the SDWH27800SS stainless-steel screw was specified for the project.

Some might consider a 316 stainless steel screw to be cost prohibitive, but when you factor in the lower cost of installation, the lower maintenance requirements and the actual cost of the fastener, this screw turned out to be the lowest cost  alternate. In addition, it provided better withdrawal and lateral load values than the spikes.

 This picture shows the deck fastening in progress. The screws are set and ready for driving with screw driving tools.

This picture shows the deck fastening in progress. The screws are set and ready for driving with screw-driving tools.

The Strong-Drive Timber-Hex SS screws made it possible to complete the deck restoration on time and on budget. Perhaps just as importantly, the pier looks beautiful and should last for many years to come.

Let us know if the comments below if you have any questions about specifying these fasteners for securing decks, docks, pilings and other heavy-duty, coastal applications.

pierdeck

As always, call our Engineering Department if you have any questions.

Have you used the SDWH27800SS screw for a project? Tell us about in the comments below.