Amid the 2017 hurricane season, we marvel at the images of the damage these forces of nature can inflict on our buildings and infrastructure. Wind speeds not only define the intensity of a tropical storm but also are one of the primary causes of damage to people and property. Taking a closer look at some of Maryland/Virginia/DC’s windiest hurricanes reveals just how significant Hurricanes Irma and Harvey were.
- 1954, Hurricane Hazel showed maximum sustained winds in Washington, DC, of 78 mph and maximum gusts of up to 90 mph.
- 1960, Hurricane Donna blew sustained winds in Maryland of 83 mph.
- 2003, Hurricane Isabel held maximum sustained winds of 58 mph and gusts of 78 mph in Maryland.
In September 2017, Irma touched down in Florida with sustained winds up to 115 mph and wind gusts up to 140 mph. Hurricane Harvey, in Texas, had similar wind speeds. These numbers are significantly higher than any tropical storm Maryland has experienced. By comparison, an even larger storm, Hurricane Andrew, overtook Florida in 1992 with peak winds at 164 mph and sustained winds at 142 mph.
The forces that hurricanes winds can apply to the structures around us is considered by structural engineers as we design buildings, renovations, and repairs. The infrequency of strong storms does not imply any insignificance to the designer, but rather the extreme forces that must be resisted. Building Code required design wind loads vary across regions of the United States based on the probable storm strength. In the D/M/V, we currently design to a wind speed of 115 mph and in Ocean City, Maryland the requirement is 130 mph for typical buildings. By comparison, Miami is in a 175 mph region and the Texas gulf coast is in a 150 mph zone.
More information on the history of damaging hurricanes, as well as the sources of the statistics in this entry, can be found in the following links.
Dust clouds created while mixing concrete, jackhammering or cutting concrete sidewalks, tuckpointing, and sawing masonry blocks will soon be a thing of the past. The Occupational Safety and Health Administration (OSHA) will begin enforcing new regulations concerning worker’s exposure to silica dust on September 23, 2017. Silica dust is commonly produced when working with concrete, brick mortar, tiles, cement board, and many other common building materials. Long term exposure to silica dust can lead to the development of lung cancer, silicosis, and other permanent conditions with long lasting consequences. Because silica dust is so prevalent, the new regulations will impact many different industries including many facets of construction. Complying with these regulations will potentially impact, property owners, engineers, contractors, and other individuals, in many ways including the cost of construction work.
While there are many requirements detailed in the regulations, contractors will have to offer medical examinations to high exposure workers, implement engineering controls for silica dust, and develop procedures to limit the exposure to silica dust that workers experience. Depending on the circumstances and activity, engineering controls can include a vacuum system with a 99% efficiency for certain cases or water methods of controlling dust. Additionally, a HEPA vacuum may be required in certain cases and a personal respiratory protection device must be supplied to workers.
Building owners, project managers, and other individuals involved with construction need to be aware of the impacts that these new requirements can have on projects. Additionally, contractors may require cooperation from building owners and managers to be able to adhere to the new requirements.
More information regarding the requirements can be found at: https://www.osha.gov/silica/
Wood construction is no longer constrained to low rise buildings and single-family homes. New uses are emerging resulting from an expanded interest in wood with new trends impacting construction. Tall wood construction has resulted in multiple high-rise wood buildings around the world from the 14 story Treet Building in Norway http://www.timberdesignandtechnology.com/treet-the-tallest-timber-framed-building-in-the-world/to the 18 story Brock Commons in Canada. http://journalofcommerce.com/Projects/News/2016/9/UBCs-Brock-Commons-rises-to-the-top-1018609W/
The interest in wood construction has led to office buildings, apartments, and commercial spaces being constructed out of wood. To support these structures, engineers have utilized advances in engineered lumber such as using glulam (glue-laminated timber), nail laminated timber, cross laminated timber, and other forms of engineered lumber. Engineered lumber is a strong wood based composite material that is often combined with special adhesives or other methods of fixation that can be used in columns, beams, and many other applications.
Renewed interest in mass timber has also risen because of the desire to construct tall wood framed buildings. It seems everything old is new again when you consider that the Old Faithful Inn was constructed in 1904 and is the largest log hotel in the world. The advances in wood engineering and higher levels of interest have resulted in investigations into potential changes to the building code that would allow taller wood construction. These trends indicate that the future of wood as a building material for both existing and new construction is exciting and filled with possibilities.
The Occupational Safety and Health Administration(OSHA) has issued new regulations regarding “Walking and Working Surfaces, and Fall Protection Systems” that have changed the requirements and responsibilities for many building owners. Building owners are impacted if they employ individuals or service providers that utilize rope descent systems that are typically called boatswain chairs and most often used by window washing contractors. OSHA issued the new regulations as part of its efforts to decrease the number of falling deaths and increase worker safety.
Without completing the necessary requirements, building owners will not be permitted to use anchor points on their buildings. Starting on November 20, 2017, buildings owners must:
· Have their anchor points certified and tested every ten (10) years by a “qualified person”
· Have a “qualified person” conduct annual inspection.
· Provide written documentation to service providers that all anchor points have been certified, inspected, and tested as detailed in OSHA Regulations (Standards-29 CFR) sections 1910.27 and 1910.66
OSHA states that a state licensed professional engineer is best for meeting the definition of a “qualified person” that is required to test, certify, and inspect the anchor points. A professional engineer would be able to determine if the anchor points can support 5000 lbs. for each individual attached, if an adequate number of anchor points exist to use accepted safe rigging practices, and if the anchor points meet the applicable code requirements. Additionally, a professional engineer can certify the anchor points by conducting an in-depth study of materials, complete performance calculations, and review installation methods as required once every 10 years by the new regulations. A visual inspection can be conducted by a professional engineer to fulfill the annual inspection requirement.
Also beginning on November 20, 2017, building owners will also be responsible for supplying written documentation to all service providers that anchor points have been tested, certify, and inspected properly before work begins. Service providers, meanwhile, will be responsible for providing assurances that necessary formal training, inspection of portable equipment, and emergency procedures are completed.
It is important that building owners impacted by these new regulations are aware of their changing responsibilities and take the necessary steps before November 20, 2017. This will prevent serious liability issue for all parties involve and ensure worker safety.
More information can be found at: https://www.osha.gov/SLTC/fallprotection/standards.html
Perhaps the nicest looking parking lot in the county just opened at our client’s apartment community. We helped add about 90 sorely needed parking spaces to solve a parking crisis at an early 1960’s vintage property. An old swimming pool had to be removed to make way for the new lot, which is complete with extensive landscaping, new LED lights, and storm water retention facilities.
If you have windows that look like this and are planning to replace them, check the caulk and glazing compound for asbestos. We have found hazardous materials in these instances and adding abatement of the asbestos can complicate a relatively simple window replacement project.
Researchers in Indonesia have developed a bendable concrete that is twice as strong as conventional concrete in bending, can be poured in thin slabs, and used for pavement. They hope that future pavement projects will be cast in a factory and slabs delivered to the job site. For information check out this link.
With Summer just around the corner, you may want to consider converting that unused roof area into a gathering spot with a beautiful view. Rooftop decks can be quite appealing, but before sending out the party invitations, make sure to consider these few helpful tips
- Hire a professional to specify maximum allowable occupants. Decks are designed for specific live loads (such as people, type of activity, snow, furniture) and specific dead loads (such as decking, pergola, railing). Therefore, design your deck for a specific number of people and specific activity.
- Ask your design professional about cross-bracing (lateral support), a very important building code requirement that affects the overall look of the deck.
- Study and understand exit requirements for your rooftop deck as specified in the building codes. Requirements for a multifamily residential building are more stringent and costlier than a single family home.
- Specify proper slope for water drainage. Our recommendation is ¼” per foot, although every situation should be carefully considered. Waterproofing of your deck and roof are very important factors of your project, if not properly built or maintained, it can cause problems and expenses for the residential unit below.
- Choose materials and construction details to last a long time. All framing should be pressure treated lumber and elevated above roofing material. Decking and railing material can be pressure treated or composite. Composite material is a mixture of sawdust, wood chips and vinyl. To keep it environmentally friendly, make sure the vinyl component is made from recycled plastic materials. Composite material is very low maintenance and there is no need for painting or staining.
- Pay special attention to lighting and controls, especially in areas such as stairs, change of levels and door entry/exit.
Is your concrete peeling or flaking in localized areas? Are you noticing rough, aggregate surfaces in your concrete that haven’t been there before, particularly after the latest round of winter weather? If so, your concrete may be experiencing a condition called scaling.
Scaling occurs when a thin layer of the concrete surface flakes, or scales, from the concrete element. Removal of this thin layer often exposes the underlying, open-pore structure of the concrete, which poses a durability concern. The most common causes of scaling are listed below.
- Non- or Low-Air-Entrained Concrete – Air-entrained concrete contains small voids which accommodate volume changes when water (i.e. precipitation) in the concrete freezes and expands. If the concrete is not properly air entrained, the concrete surface may be overcome by expansive forces during freeze-thaw cycles, resulting in loss of material.
- Unsuitable Concrete Mix – Concrete mixes with low strength (less than 4,000 psi in exterior, exposed conditions) or those with high water-to-cement ratios are more susceptible to water intrusion and deterioration.
- Excessive/Improper Deicing Agents – These chemicals can attack surface layers of concrete. These chemicals can also create brines (which have lower freezing points than fresh water), and can increase the number of freeze-thaw cycles.
- Poor Finishing – Overworked concrete surfaces or those that receive additional water and or finished with bleed water can result in reduced entrained air content or weak, thin, cementitious paste deposits at surfaces.
Repairing scaled concrete surfaces can prove difficult. If a proper bond is not achieved between the cementitious topping/overlay and the underlying concrete, additional scaling or delamination may occur. If scaling is prevalent in your community, contact a professional engineer to determine the extent of the damage and to develop the proper repair strategy.
Have you noticed dry, powdery deposits on the concrete elements in your community? Or have you walked across concrete and had a white, dust-like powder follow you? If so, your concrete may be experiencing a condition called dusting.
Dusting occurs when the surface of concrete disintegrates, resulting in a loose, chalk-like powder. A list of potential causes of dusting is provided below.
- Poor Finishing – The addition of too much moisture during finishing operations, or condensation of cool air on the fresh, warm concrete surface can result in a weak surface layer. As pedestrian or foot traffic is applied to this soft surface, dusting may result.
- Poor Placement Conditions – Improper ventilation in an enclosed space where machines producing carbon dioxide are present, such as a garage, could result in carbonation of the concrete. This chemical reaction reduces the concrete strength, which may lead to chalking surfaces.
- Improper Curing – The omission of moist curing (i.e. wet burlap) operations or approved curing compounds can allow the surface of fresh concrete to dry out, resulting in a soft surface, susceptible to disintegration.
- Insufficient Protection – Newly placed concrete subjected to an unexpected summer rain storm, high winds, or freezing overnight temperatures without proper protection are prone to weakened surfaces and even reduced strength.
The good news is repairing this condition can be relatively routine. Sandblasting or pressure washing can remove the soft surface, or applying a hardener or sealer may also be effective. However, if the dusting/surface deterioration is severe, application of an overlay or topping may be necessary. If your community is experiencing dusting or you have concerns with your new concrete, consult with a professional engineer who can help evaluate and determine the appropriate repair solution.
Due to our growing need for space, we have relocated our Columbia office. Please note the address & phone number change…we would hate to miss your call!
A common deterrent to personal enjoyment in multi-family buildings is sound transmission. Often determining what is too loud is subjective and measured by the sensitivity of our ears. The Building Code requires that walls and ceilings meet an STC (Sound Transmission Class) rating of 50 and an IIC (Impact Insulation Class) of 50. STC is related to airborne noise like a television, speech, or music and IIC correlates to footfalls or a dog’s toenails when they impact a tile floor.
At an STC rating of 50, loud talking cannot be heard but load music can be noticed. We usually are asked to investigate sound transmission concerns in wood framed buildings when the thuds of foot traffic of the resident or their pet, above, is perceived to be disturbingly excessive. Many condominiums have rules related to the percentage of the floor area that must be covered by carpet. This is likely because most carpeted floors comply with a IIC 50 sound rating.
Manufacturers of products used to construct wall and ceiling assemblies have their materials tested in a laboratory with various combinations of framing, drywall, and insulation to determine the STC rating. To inspect a noise concern, our first step is to review the available architectural drawings to determine the intended design and the associated STC rating for the wall and/or ceiling construction. Then we will cut a few holes at inconspicuous places to confirm if the drawings were followed. Most people are surprised to learn that no insulation was placed inside the wall or ceiling and that many assemblies can achieve the required STC rating without insulation.
Products are available that can be installed on floors, walls, and ceilings to reduce the offending sound transmission. Installing these materials can be limited to sleeping areas to save cost and the amount of disruption that the project has on a living space.
Satisfactory remediation of a sound problem can be difficult. Our ears will perceive a reduction in noise by one half when the STC rating is increased by about 10 points. Conversely, anything less than a10 point change is hard for people to distinguish. Finally, any expectation that a once noisy unit located within a multi-family building will become “sound proof” or like a recording studio after remedial work is complete is unrealistic