PEC engineers routinely work with industrial and petrochemical clients and their contracted architects and engineers to incorporate protection from industrial hazards and accidental explosions into facility designs and existing facilities. These hazards, deflagrations and explosions of compounds and gases result in low to moderate pressure loads on buildings, but have relatively long durations as compared to “traditional” high yield explosives. In addition to being designed for different “loads”, the required protection levels for industrial and petrochemical facilities are generally more stringent due to greater probability of occurrence of the hazard and due to the need for continued operation and control at these facilities after an event. This blast-resistant design objective is called a “shelter-in-place” performance level, which provides protection for facility staff and assures structural integrity of the building in order to protect critical equipment and operations. We have experience designing new control rooms and structural retrofits for existing buildings at petrochemical plants and industrial facilities in the United States, Canada, and the Near and Middle East.
Retrofit of Existing Facilities—Retrofit design projects involve the assessment (analysis) of typically older unreinforced masonry buildings or lightweight pre-engineered buildings. As a first step, we perform analysis of these existing structures to evaluate the current level of performance against specified overpressure loads. Individual components (walls, windows, openings) are analyzed, as well as connections between components and the lateral load resisting system of the building (roof diaphragm, moment resisting frame, shear walls). These components may lack the capacity to provide the required level of protection at the specified overpressure design loads. If the calculated performance level is unacceptable, concept level designs are developed for two or three different retrofit options that will resist the design blast load with an acceptable level of performance. This work can include cost estimates for each concept that is approved by the client. Retrofits might include wall strengthening using fiber-reinforced polymer (FRP) composites or through attachment of vertical steel posts on the exterior surface of masonry walls. Another option for protection might include the design and construction of a blast-resistant shield wall outside of but very near the existing wall. As a part of our overall design services, we provide guidelines and recommendations for retrofitting or replacing windows, doors, and air transfer louvers. When requested, we also consider non-blast threats such as debris impact from hurricane hazards.
Design of New Control, Operations and Administration Facilities—For new construction, or when the assessment of an existing building indicates that it is more efficient to replace the building than retrofit it, we work closely with the architect and structural engineer to design a blast resistant building that satisfies prescribed overpressure and shelter-in-place requirements. Structural gravity and lateral systems for new buildings include cast-in-place concrete frame systems, cast-in-place exterior load bearing wall systems, and steel frame systems with exterior precast concrete panels. Roof systems may consist of steel beams, joists, concrete framing and cast-in-place deck, and composite steel and concrete deck systems. In some cases, prefabricated steel buildings are also employed.
Tools, Methods and Criteria—Our engineers follow the analysis and design approaches of ASCE’s “Design of Blast-Resistant Buildings in Petrochemical Facilities” (2010). If fact, Chuck Oswald authored Section 10.3 of this document titled “Upgrades to Existing Buildings”. We also draw upon general blast design experience for anti-terrorism and weapons effects protection and incorporate analysis and design approaches from other guidelines, such as UFC 3-340-02, as appropriate. Analysis and design of building structural components is done using nonlinear dynamic analysis. Structural components directly loaded by the blast load are analyzed using SDOF (Single-Degree-Of-Freedom) analysis. PEC uses the SBEDS (Single-Degree-of-Freedom Blast Effects Design Spreadsheet) computer program distributed by the Protective Design Center of the U.S. Army Corps of Engineers (PDC). The SDOF analysis is also used to determine equivalent static reaction loads, which are used to design connections using conventional static design methods from applicable design codes (ACI 318, AISC manual, PCI design handbook, etc.)
When required, we evaluate the overall lateral “sway” response of moment-resisting frame structures due to overpressure blast loads using nonlinear dynamic analysis. We can use SDOF methods for approximate analysis of simple frames or can evaluate the dynamic response of more complex frames with nonlinear dynamic analyses in codes such as SAP2000 or LS-DYNA.