Case Narrative. Foundation Wall System The site of the dining hall sloped quite significantly from front to back, so it was necessary to level the area. The design called for the bottom floor to be level with the elevation at the back of the site and the top two floors to be built up when looking at the front of the site. This required that the whole site had to be excavated down to the depth at the back of the site. When working in the excavated area, there was a risk for those workers to be struck by falling objects or pieces of equipment. Benching the walls of the excavation site added an extra measure of safety and sharply decreased the likelihood of a cave-in or an instance of falling equipment. Caissons were chosen as the foundation for the dining hall due to the type of soil in the area as well as the precedent set by existing buildings constructed in the area. To help minimize the safety risks, workers were trained in the proper procedures for installing the deep foundation. A retaining wall was needed at the front of the building, as the back of the building was at grade while the front of the building was at the 2nd story. Cast-in-place concrete was chosen for the front wall of the building during the design development phase. This was chosen over masonry because of the reduced cost and speed of construction of this type of structure versus masonry. This was also safer for workers because it did not involve as many workers in an enclosed space or at heights during construction of the wall. One mechanism to allow for material laydown at the front of the site was to backfill the front retaining wall early so that the backfill was at grade at the front of the site. The original drawings from the structural engineer stated that the steel superstructure and floor of the first level needed to be braced before the wall could be backfilled. The CM asked for the structural engineer to determine what would be required to allow for the retaining wall to be backfilled before the steel was installed. The structural engineer stated that the retaining wall would have needed increased temporary bracing to allow the backfill to be completed before the 1st floor structure and floor were completed. This cost would have had to have been absorbed by the CM, as it would have been a change the owner would not have paid for. The CM said that once they got far enough along in the design they were able to determine that the front storage would not be required, and the extra cost of the t...
Case Narrative. Haul Road A haul road was used to transport materials and equipment along the project corridor. The haul road to the site was limited in size to a single lane design due to the smaller construction footprint. Maintenance of the haul road over time was necessary in order to keep it open and accessible at all times during construction. During this phase, there was risk for workers to be struck, caught in, or compressed by equipment or objects. This was solved by the constructor implementing communication between workers and drivers as an administrative control. Using stone and grading allowed for the road surface to remain safe and prevent instances of slips, trips, or falls. Temporary Bridges Since the project corridor traversed wetlands and creeks, temporary bridges needed to be built to allow movement of equipment and materials. To ensure the safety of workers on the bridge, the CM needed to take measures to prevent falls or being struck by equipment or vehicles. Instead of delegating fall protection to the subs, the CM had temporary walls put up along the bridges to meet OSHA requirements for fall protection. The design width of the bridges eliminated the risk of workers being struck by equipment or vehicles, although signage, temporary barricades, and communication between workers and drivers were still utilized to ensure worker safety.
Case Narrative. Site Excavation When excavating the deep and wide area for the foundation and basement of the house, there was a cave-in hazard for workers. This was eliminated by the constructor’s decision to have the sides of the excavation benched.
Case Narrative. Site Excavation A basement was decided to be included in the site excavation. As both the designer and operation manager (OM) noted, the local market used to have one in typical residential houses. It is because of the area topography which lent itself to a basement since most lots have a slope. Also, the client also dictated this decision based on their needs. The DB team chose benching and sloping methods for site excavation. This type of method is simpler and costs less than other control methods that would require temporary shoring and bracing. The builder had worked with the same excavator for years (they tried to do this with all of their trade subcontractors because they felt it allows the subs to better understand their requirements), and typically gave them the depth and area of the excavation that was needed. The designer said that he had a pre-construction meeting on site with the excavator to discuss a grading plan, but the OM said that they like to rely on the subcontractor’s expertise. The OM said that they are basically paying for the time the "machine is on", but they gave the excavator latitude on the height of the bench, layback, and sloping because they trusted and preferred them to do what was required to safely perform the work. The builder’s policy is to over-excavate four feet past the wall lines to allow a sufficient setback for subs to work safely and efficiently in the area. This cost a little more on excavation, but allowed sufficient room for the forms to be safely maneuvered and eliminated cave-in hazard at the work face.
Case Narrative. Pre-cast Concrete Panel Design To match other buildings and for cost-saving purposes, pre-cast concrete panels were chosen for the outside façade of the building. The only other option explored was using pre-cast concrete panels to window sill height (±3’-6”) and then use cement plank siding on metal stud framing above the present height. For aesthetic reasons, the architect advocated against the siding option. The building design was configured with three enclosed outside courtyards. The courtyard walls were pre-cast concrete panels to match the exterior façade of the rest of the building. One difference between the interior courtyard design and the building exterior were larger windows on the exterior allowing more natural light in for patients without access to the courtyards. The diversity of window sizes affected the design solution by reducing panel standardization and resulting in additional panels of varying sizes and increased complexity in panel connections. The decision was made to have the pre-cast concrete panels manufactured to the full building height where possible in order to minimize the total number of deliveries and lifts required for installation. This was a scheduling decision, but it did also have an effect on safety since fewer deliveries and lifts mean fewer opportunities for incidents. Shear Wall Design The original building design included a shear wall design requiring shear panels to have a direct connection to the footing. Non-load bearing panels were designed to connect to a one foot high concrete stemwall. The CM and pre-cast panel subcontractor made a recommendation during the construction drawing phase to eliminate the stemwall and connect all panels to the foundation. This increased panel lengths by one foot and allowed elimination of the concrete stemwall. The PM said this eliminated remedial xxxx-hammering and sawing of the stemwall to vertically align all panels. The net effect is faster and safer construction. This decision was made primarily due to constructability and scheduling, and the CM said the original design could have been made to have direct footing connections. Pre-cast Panel Installation One of the key decisions that affected the panel installation was the logistics of the structural steel erection. It was decided by the CM to start installation at one building wing and work clockwise wing by wing. This plan allowed the panels to be installed simultaneously with the wing framing once the structural steel f...
Case Narrative. Federal and state governments gave a utility consent decree that wastewater system must be upgraded to meet certain capacity requirements due to reported overflows in the wastewater system. The utility responded to the consent decree and the response was accepted by the government. The accepted consent decree requires the utility to improve the wastewater system so that the overflows within the system are reduced to levels that meet regulatory requirements. Once the consent decree was accepted the utility was required to develop an engineering improvement plan with a list of projects to increase capacity and eliminate chronic overflow locations within the system. The utility used a flow model of the system to test different options and determine which list of projects increased capacity in the most effective way versus their respective cost. The projects were broken up into sewer basins, and each project is dependent on others (thus the projects must be evaluated as a whole). Public meetings were held for input, and a public committee was formed to give input into the process. Another part of the consent decree was a requirement to upgrade sewer treatment plants to meet anticipated peak flow volume based on system improvements and anticipated new connections to the system. The system evaluated the capacity needed at the WW plant based on worst case conditions, and developed a list of options to increase capacity to the required levels from the model. Nine alternatives were identified for the WWTP. Each of these potential improvement alternatives was first developed to a conceptual level. At the conceptual level the alternatives were screened to rule out those that were considered by the utility not to be feasible due to operational, site, or treatment constraints. Also as part of the screening analysis, each alternative was evaluated in terms of costs and non-monetary factors to determine if the alternative should be considered further for analysis. This was done by ranking the options 1-5. Next, the screened alternatives were developed further to generate preliminary design and flow diagrams, hydraulic profiles, plant layouts, and preliminary cost estimates. Table 4-9 shows the list of improvement projects required for each of the options that were further evaluated after screening. Cost estimates and preliminary design drawings were then developed for each of the options for further evaluation. Option 3 was chosen based on both cost and the ability to ef...
