I’m Digging Your Shoring Plan!

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Due to the complexity and property line constraints of modern construction, earth shoring requires a solution that must conform to both engineering and safety guidelines during all stages of construction.

Here are the key concepts to remember for an earth shoring design:

  1. Applicable codes: The type of project will define the requirements for an engineered earth shoring plan. For instance, a design that allows for inches of deflection at a multi-story urban high-rise may not be compatible with AREMA requirements for railroad earth shoring. While a contractor may be able to get away with using a cantilevered design, a similar design that incorporates the locomotive surcharge loads into the analysis may fail simply by being out of tolerance for railroad deflection guidelines. In this case, the common solution is to add soil anchors to keep the design in compliance.
  2. Material: This is typically a contractor preference. If a contractor has a substantial inventory of steel I-beams/H-piles and wood lagging, it is in the best interest of the client for the engineer to design the system accordingly. Piles may need to be spaced more tightly and the design may not be as efficient as sheet piles, but it does eliminate the need for the contractor to spend more money.
  3. Sequencing: With most earth shoring designs, there is a sequence of installation that must be followed based on the applied loads that change with depth. For example, in a cofferdam design, if wale frames are required, the contractor may have to install the wale at a specified elevation prior to proceeding. This elevation may be above the final excavation depth, but the engineer should have determined that this is the maximum depth that the shoring can support in a cantilevered condition and/or without restraint at the base. This may be a result of deep excavations where the substrate alone at the base is not adequate to support the lateral load. Oftentimes, many scenarios must be analyzed to ensure that the members are not overloaded and the entire shoring design is code-compliant at any given stage.
  4. Embedment Depth: As a general guideline, the minimum embedment depth of a pile must be 75% of the retained height to ensure adequate development and base restraint.
  5. Workers at the Top of the Excavation:  While the designer may account for the surcharge loads at the top of the excavation, it is also important to consider the impact of workers. If a guardrail is required based on project conditions, then it must be OSHA compliant and any loads/connections required shall be accounted for in the design of the pile. Common practice is to weld a guardrail post at the top of the pile, but this must be checked not only for load application, but also for maximum spacing.

Engineered shoring plans are critical components of construction plans, and a well-thought out design will save the contractor both time and money. As the saying goes,”Think before you dig!”

5 Impressive Things Built (or Fixed) Using Cofferdams

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Everyone knows about dams. But have you heard about a cofferdam?

Cofferdams have been around for a long time. People have used these when excavating very large plots of land or building foundations of water-based structures such as bridges or piers. The cofferdam keeps water from flowing into these sites, ensuring a dry foundation.

The cofferdam has been used to build and fix some impressive things. Check out the five most inspiring objects constructed by using these fascinating dams.

5 Impressive Things Built (or Fixed) Using Cofferdams

Cofferdams have helped civilizations divert water, gain new territory, build dry structures safely, and even recover history. They can be as simple as a pile of sandbags set up to use as a barrier during wartime or complex as a double sheet piling used in modern-day bridge construction.

While today the cofferdam is particularly useful for earth shoring engineering projects, it continues to be used in the engineering world as a helpful tool in water diversion projects.

1. Battleship U.S.S. North Carolina

Because ships are a water-borne craft, their preservation often depends upon a dry work environment. When it comes to this battleship located in Wilmington, North Carolina, the use of a cofferdam will integrate a memorial walkway for visitors and water-free access to the battleship for preservation and repair work.

The project, nearly six months away from completion, is unique because it won’t rely on the cofferdam for underwater construction. This battleship will be open to visitors and kept looking sharp above water.

While this battleship will cost a hefty $8 million, it will, in fact, be a permanent installment. This is another great aspect of the cofferdam: it can be both temporary or fixed. The permanent cofferdam enables future maintenance and repair work on structures like the U.S.S. North Carolina.

2. The Hoover Dam

It may seem counterintuitive to say that dams are made by using dams. But with this impressive dam that’s become an icon of the American road map, cofferdams were a huge part of the construction.

The Hoover Dam construction was an architectural and engineering feat in Nevada in 1933. Before the dams were installed, workers removed 250,000 cubic yards of silt from the river in order to ensure a solid starting foundation.

Two cofferdams were required to make sure the construction was dry and water-free. Both were made from earth and rockfill, and relied on an additional rock barrier to prevent any additional water seepage. While some people were worried that the spring Nevada floods may damage all of this foundation pre-work, the damming worked and construction went along as planned.

3. Ancient Roman Bridges

When we said that the cofferdam has been around for a really long time, we meant it. For thousands of years, civilizations have found the cofferdam useful, and you see this in many of the bridges of Ancient Rome.

Early populations relied on more basic forms of the cofferdam in order to control waters for drinking supply, irrigation, and land control. Often this entailed the diversion of a river. Legend has it that King Cyrus of Persia used the cofferdam in order to divert the Euphrates River in his pursuit of the city of Babylon. This meant that an entirely new empire was established based off of the use of this dam alone!

Similarly, the Romans made use of this handy type of damming when bridging the Danube River. Trajan’s Bridge, built as a result of cofferdam wood pilings, enabled the Romans to travel to contemporary Romania. This bridge totaled nearly 4500 feet in length.

4. The Tapan Zee Bridge, New York City

The Tapan Zee provides a great example of how cofferdams still help with important construction feats today. This incredible bridge spanning the Hudson River cost nearly $4 billion to construct. Its completion would not have been possible without the use of the cofferdam.

A complex software was used to design the steel dams, 90 feet by 45 feet, used in construction. The software also took soil type into consideration. Because the Hudson contains a lot of river silt and soft deposits, the Tapan Zee dams had to be backfilled in order to create a solid base for the bridge piers.

5. The La Belle ship

The La Belle shipwreck has long been an icon of the Texas coast, and the cofferdam made sure that La Belle remained a fixture of seventeenth-century history.

In 1687, this ship crashed along the shoreline as a result of poor weather and difficult seas. Manned by a New World explorer, this ship was the last of four ships sent to explore the unknown coasts. When La Belle crashed and sank, it became sealed in mud for over three hundred years.

In 1995, an archeological team discovered the site of La Belle’s sinking. Such a recovery requires a lot of complicated engineering. The Texas Historical Commission constructed a cofferdam system around the sunken ship. This elaborate system cost over $2 million.

The mission was successful, and in 1997 the full extent of the treasure was known. Hundreds of incredibly preserved artifacts and much of the ship’s original structure were recovered. If it weren’t for the cofferdam, we would never know this history.

Cofferdams of the Future

There’s no doubt about it: the cofferdam is versatile, useful, and amazing. It has enabled people to bring history back to the surface, cross rivers, and construct impressive architecture. The cofferdam will continue to be an essential part of contemporary engineering projects.

At DH Glabe & Associates, cofferdams are our bread and butter when it comes to earth shoring engineering. To date, we’ve completed over five thousand company projects in thirty-two years, relying on the expertise of over fifty professional licenses. We assist with both civil and commercial projects using a variety of technology, including H-piles, mechanically stabilized earth walls, sheet piles, geofabric, and secant pile walls.

Earth shoring is not all we do. No matter the size or type of your engineering project, at DH Glabe & Associates we pledge to be with you every step of the way. Contact any of our construction engineering experts today to learn about what we can do turn your project into a reality this year.

What You Need to Know: Earthquake Resistant Buildings

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Earthquake resistant buildings save lives. They limit property damage and comply with the latest seismic building codes.

If you do business in high earthquake hazard areas, here’s what you need to know about seismic building codes.

1. Seismic Building Codes are Getting Tougher

In 2015, Los Angeles overhauled their seismic regulations. 15,000 buildings needed retrofitting to better withstand the effects of earthquakes.

For decades, safety advocates worked to pass ordinances strengthening two types of structures. First were the brittle concrete buildings on L.A.’s major boulevards. Second, the boxy wood-frame apartment buildings built on top of carports. Over 65 people died when these types of buildings collapsed during earthquakes in 1971 and 1994.

2. Designing Earthquake Resistant Buildings is a Regional Endeavor

Building codes are based on the base shear formula. This formula measures how much earthquake-generated shear force will try to push the house off the foundation base. The simple formula multiplies the expected ground acceleration by the building’s weight.

But there’s no set amount for anticipated ground acceleration. For example, Los Angeles anticipates a different base shear than the California Building Code does.  The International Existing Code’s ground acceleration is different still. Keeping this in mind, it’s always best to use a base shear that’s tailored to your geographic region.

3. It’s Not Just the Building, It’s The Ground Underneath

Earthquake resistant buildings are great. But let’s say a building’s foundation sits on soft soil. Despite the advanced engineering techniques used, it could still collapse in an earthquake.

But, if the soil beneath a structure is solid, engineers can improve how the entire building foundation system responds to seismic activity.

One example is base isolation. In this method, a building is floated above the foundation on bearings, springs or padded cylinders. A solid lead core is used for vertical strength with rubber and steel bands for horizontal flexibility. This allows the foundation to move without moving the structure above.

4. Seismic Engineering has a Bright Future

All around the world are examples of newer structures withstanding earthquakes. One example is the Transamerica Pyramid in San Francisco.

During the Loma Prieta quake, the building shook for more than a minute and the top floor swayed a foot side to side. A deep concrete and steel foundation and a buttressed exterior allowed the building to escape structural damage.

Sensor readings were taken from the building’s frame and processed by the U.S. Geological Survey. The results showed the building could withstand an even larger seismic event.

The future of seismic engineering doesn’t just look forward. Retrofitting older buildings is as important as new construction. One bright spot is engineers are effectively and economically adding base-isolation systems to existing structures.

After the 1989 Loma Prieta quake, engineers retrofitted the city halls of San Francisco, Oakland, and Los Angeles. These earthquake-resistant structures will be tested. When and how remains to be seen.

The Final Analysis

More jurisdictions are mandating seismic building code compliance. That’s where DHG comes in. Our experience with earthquake resistant design ensures your clients’ buildings will comply with the latest codes.

To see our seismic engineering services up close, contact us for a consultation.

Is Visual Inspection Still A Safe Method?

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Visual InspectionTechnology continues to change the way we both live and work. So it’s no surprise that safety and inspection tools have become sharper, more precise, and more high-tech than ever before.

Yet, though these digital advancements can prove invaluable, there is still a place for visual inspection. Not only is it still a safe method, it’s an important step in the safety validation process.

Today, we’re taking a closer look at this inspection procedure, and detailing how it remains a safe, viable quality control (QC) solution.

Ready to get started? Let’s dig in!

Visual Inspection: The Original QC Procedure

There are now more complex and intricate tools on the market. Yet, the reality remains that visual inspection is one of the most basic and traditional QC procedures.

It’s important to delve deep into an object to ensure total safety and security. Yet, by simply looking at an object, the reviewer can quickly and easily note anything that looks incorrect or flawed from the naked eye. If it doesn’t meet an Acceptable Quality Level or another parameter, it can be sent back for adjustment.

This helps make the QC review process more effective and promotes stronger teamwork. Otherwise, a reviewer may be knee-deep in a resource-draining QC procedure before an issue is realized. Catching the issue at the forefront can result in a smoother and more collaborative review.

An Inexpensive and Accurate Way to Measure

If a trained and certified inspector performs a visual inspection, it can be as effective as a more elaborate non-destructive QC review. It is also incredibly simple and more cost-effective to perform.

These types of inspections require almost no equipment. There are tools that can be used to enhance visual testing examinations. These include magnifying glasses or even remote viewing computer systems. Yet, they can also be performed with no tools at all.

This means a safer review, as there is less risk of an operator injury. It also means there are little to no costs involved in the process. It’s also quicker and easier to perform, saving an organization both time and money.

In the Details: The Advantage of the Human Eye

There are tools, such as a dimension inspector, that can verify if an object’s dimensions and measurements are correct. This is an important part of the overall QC process, but often, important details are omitted.

What a majority of these tools fail to measure is the visual representation of the object. For instance, a cube’s measurements may be accurate, but what if one of the sides is cut or damaged? Similarly, what if the final product is measured and cut correctly, but is actually a reverse image from what was originally agreed upon?

Visual inspection can notice these discrepancies, even where an intelligent machine cannot. As such, it’s an important step in keeping systems (and their users) safe.  

Expert Engineering: Quality You Can Trust

As a Nationwide Leader in Structural and Construction Engineering, we know a thing or two about quality. We pride ourselves in providing top-notch services for myriad engineering needs such as concrete shoring, earth shoring, wall bracing, formwork, falsework and many other Construction Engineering Services.

If you’d like to make sure your next project is sound and secure, we’d love to help. Feel free to contact us or leave a comment below and let’s build something great together!

Stresses of Thermal Loads

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A thermal load is defined as the temperature that causes the effect on buildings and structures, such as outdoor air temperature, solar radiation, underground temperature, indoor air temperature and the heat source equipment inside the building.

ASCE 7-15 section 2.3.5 and 2.4.4 specifically mention thermal and other self-straining loads are to be considered, where applicable. For many cases, thermal movements cannot be restrained and instead designs need to allow for the structure/equipment to move thermally otherwise stresses in either the restraints or in the structure/equipment may cause catastrophic failures.

Different materials have different expansion rates. Structures or items with different types of materials connected by fasteners or adhesives can warp and break at extreme temperatures. For example, PE pipe will expand/contract around ten times more than steel pipe.

Historically, thermal stresses have caused failures in railroad tracks, roads and building facades and even electronic devices. Understanding these effects, and how to minimize them, reduces the risk of damage or failure at extreme temperatures and prevents having to perform costly repairs.

For example, a 200 ft long PE pipe can change in length by 1/8 of an inch per degree (F) of temperature change. If this movement is restrained, stresses in the pipe and the restraints will be generated. Depending on the strength of the restraint and the buckling strength of the pipe, the restraint could fracture or the pipe could buckle. Buckling pipes can injure anyone working next to the pipe and could also cause leaking of the pipe. Damage and injury could also occur when a restraint breaks.

Even sidewalks are not immune from thermal stresses. Recently a large section of 4’ wide sidewalk was installed about a block long. Thermal expansion joints were not provided at adequate spacing. During a hot summer day, a loud explosion was heard throughout the neighborhood. The sidewalk had buckled and one of the sections of sidewalk had shattered. The concrete was left uneven and damaged requiring removal and repair of the damaged area of the sidewalk. Additional thermal expansion joints were provided to hopefully prevent future problems.