Nothing like a rainy day to see how one of our drainage projects is performing. The channel is not done. We still need some plants to finish the step pools to make the swale look even prettier.
About Chris Carlson, PE
Posts by Chris Carlson, PE:
It is too early to tell what might have failed and caused this bridge to collapse and it will probably be many months before the investigation is complete. The bridge was designed to consist of post-tensioned concrete segments supported by steel cables. It was to have been built in two sections and only the first section was in place when the collapse occurred. The first section of the bridge had only been in place for five days before it fell, so it is not likely a case of being grossly under-designed or inadequate concrete strength. One report indicated that the post-tension tendons had loosened and were being retightened when it fell.
Institutional and government projects like this have many levels of design review and material testing involved to help ensure public safety and that the 100-year design life is achieved. This bridge was far from complete as there was a central support pier (pylon) for the steel cables that still needed to be installed. This pier and the cables would have provided additional support to the failed section of the bridge. Partially constructed structures can be very dangerous.
This catastrophic failure reminds us of the inherent hazards of all construction work, not just those involved with demolishing and rehabilitating portions of existing structures. Our prayers go out to all those involved in this tragedy.
Before any rope descent system (i.e., window washing boatswain chair) is used on a building, OSHA now requires that each anchor be identified, tested, certified, and maintained so it is capable of supporting at least 5,000 pounds in any direction.
Did all your anchors pass the test?
The OSHA set November 20, 2017 deadline for physical load testing of these anchors has passed. (29 CFR 1910.27(b)(1)(iii)).
Did you make the deadline?
We loaded anchors of many different configurations and found that not all anchors passed this stringent test. If you have any anchors that have not been subjected to this testing in the last 10 years, they must be load tested and certified by a qualified person before they are used. This regulation also seems to apply to new anchors that were installed after the November 20 deadline and not just older anchors.
Don’t postpone your scheduled winter or spring window washing work, get your anchors tested soon. Call us @ 410-312-4761 or 703-450-622o | email@example.com
Fall weather has revealed many areaways that have inadequate drainage because the drain grate clogs easily. It often takes just a leaf of two to slow down the flow on these small grates. Provide more margin against rising water and flooding interiors by installing larger drains. Not only will the larger drain remove water faster, it can become partially clogged and still have adequate flow to keep the water from entering under the door.
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.
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.
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
Perforated PVC pipes used for underground drainage have offset holes drilled along the centerline of the pipe. It seems that some philosophical disagreements exist related to the placement of the holes in gravel filled trenches (i.e. French Drains). A review of installation instructions from several State DOT manuals reveals that the holes should be down (i.e. placed facing the bottom of the trench). The reason is that this allows the water to enter the pipe and drain from the soil at the lowest level. If the holes are located along the top of the pipe, then the water must rise to the level of the top of the pipe before it can be drained. In most cases, the purpose of these buried pipes is to collect water in the ground before it enters a building basement or seeps up through parking lot pavement, so it makes sense to collect the water at the lowest level available. Water will follow the path of least resistance, so once it enters the pipe, gravity will make it travel until it reaches the discharge point at the low end of the pipe.
Researchers at the Delft University of Technology in the Netherlands are working on placing bacteria in concrete mixes to fix cracks in concrete and make it self-healing. This could make concrete less susceptible to damage related to water that infiltrates a beam by way of a crack and results in rebar corrosion.