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Design Loads on StructuresDuring ConstructionASCE 37-14

Design Loads During ConstructionPurpose of this presentation is to become familiar withASCE 37-14, including: Types of Loads to consider during design Terminology used in the Standard Consideration of wind loads and how reduced windloads may be used for selected project parameters Specific example of wind load in a “hurricane pronearea” 2 examples along the Gulf Coast where a structuralcollapse occurred during construction

Design Loads During ConstructionSAFETY CONSEQUENCESOSHA investigated 96 structural collapses duringconstruction involving fatalities and injuries over theperiod from 1990 to 2008 80% were caused by construction errors (ex. not followinginstallation procedures, did not provide temporary bracing, etc.) 20% were attributed to structural design flaws by either EOR or astructural engineer retained by a contractor to design specificmembers Largest group of collapses involved steel structures (includingscaffolding), followed by concrete & masonry structures, and thenwood frames (example: roof trusses)

Design Loads During ConstructionASCE 37-14Design Loads on Structures during Construction1st edition of Standardpublished 2002Latest edition is 2014

Design Loads During ConstructionPurpose of ASCE 37-14 is to provide minimumdesign loads during construction of buildings andother structuresScope is for Partially completed structures Temporary structuresASCE 37-14 Standard does not: Specify party responsible for design of temporarystructures Specify party responsible for on-site supervision

Design Loads During ConstructionTypes of Loads Dead Live Construction – equipment, materials, personnel Environmental – wind, snow, rain, earthquake Hydrotest – piping and/or equipment Lateral earth pressure Forces from interaction of partially completedstructures and temporary supports or bracing

Design Loads During ConstructionConstruction Loads Materials Equipment Personnel Erection and Fitting forces Dead load of permanent structures are included inDead Load (D)

Design Loads During ConstructionConstruction Material Loads Fixed (FML) – fixed in magnitude Variable (VML) – loads that vary in magnitude duringthe construction processArea of application may be distributed or concentratedExample of variable loads: stockpiling and stacking ofrebar, roofing materials, drywall, etc.Example of fixed material load: formwork once itsinstalled

Design Loads During ConstructionCast in Place Concrete Concrete placed in a form is initially considered as amaterial load Once concrete gains sufficient strength so that formsand shoring may be removed then it becomes a DLForm pressure Cc (lateral pressure) wh (lbs/ft2)w unit weight of fresh concrete, lbs./ft3h depth from top of placement to point ofconsideration, ft.Specific formula for form pressure of concrete columns

Design Loads During ConstructionPersonnel and Equipment Loads

Design Loads During ConstructionHorizontal Construction Load, CH Wheeled vehicles transporting materials, 20% for asingle vehicle, or 10% for 2 or more vehicles of afully loaded vehicle weight Equipment reactions, calculated or rated horizontalloads (whichever are greater) 50 lbs/person, applied at the level of the platform 2% of the total vertical load, need not be appliedconcurrently with wind or seismic load

Design Loads During ConstructionWorking Surfaces – floors, decks, or platforms oftemporary or partially completed structuressubjected to construction loads

Design Loads During ConstructionDesign Wind Loads are based on Construction Period

Design Loads During ConstructionWind Design in Hurricane Prone Areas, twoperiods of time are considered for construction November 1 to June 30 (outside of hurricane season) July 1 to October 31 (during hurricane season). Note thisdefinition is different than that used by the NHC, which is June 1to November 30 for the Atlantic, Caribbean and Gulf of Mexico

Design Loads During ConstructionHurricane Prone Areas, period from November1 to June 30 (outside of hurricane season)

Design Loads During ConstructionHurricane Prone Areas, period from July 1to October 31(during hurricane season)

Design Loads During ConstructionExample of Wind Speed calculations Project location: Theodore, AL (Mobile County) Risk Category II, open frame structure Construction duration: 6 months V 159 mph (ASCE 7-10); source: ASCE Hazard Tool Construction outside of hurricane seasonUse V 115 mph x 0.8 (factor from 6.2.1) 92 mph Construction during hurricane seasonUse V 115 mph with additional bracing

Design Loads During ConstructionWind – Continuously Monitored Work Period Intended for periods of continuous rigging, erectionor demolition that last for one work day or less Example: lifting of girders, columns, façade panels,equipment may use temporary guy wires, struts,minimum number of fasteners, etc. At end of work day the structure shall be madeinherently stable or secured, to meet therequirements previously outlined

Design Loads During ConstructionWind – Continuously Monitored Work Period(continued) For continuously monitored work periods a lowerwind speed may be used Wind speed to be used shall be based on theNational Weather Service or another reliable sourceacceptable to the authority having jurisdiction The basic wind speed shall not be less than thepredicted wind speed adjusted to the 3-second gustspeed multiplied by 1.26

Design Loads During ConstructionFramework without Cladding – effects ofShielding Even though design wind speed during constructionmay be lower than for the completed structure, thetotal wind load may actually be higher due to thecumulative effect of wind acting on more surfaces For common arrangements of elements in typicalopen frame and temporary structures the shieldingeffects are small Most severe wind loads on an open structure includecomponents of load in both principal directions

Design Loads During ConstructionFramework without Cladding – effects ofShielding (continued)Load reductions due to shielding The loads on the first 3 rows of elements along thedirection parallel to the wind shall not be reducedfor shielding The loads on the 4th and subsequent rows shall bepermitted to be reduced by 15% Wind loads shall be calculated for all exposedinterior partitions, construction materials, equipment

Design Loads During ConstructionFramework without Cladding – effects ofShielding (continued) Calculations shall be performed for each primaryaxis of the structure For each calculation, 50% of the wind load calculatedfor the perpendicular direction shall be assumed toact simultaneously

Design Loads During ConstructionThermal LoadsProvisions shall be made for thermal distortions of thestructure and architectural components. Formula isbased on the following: Largest horizontal dimension between expansionjoints of the erected structures Difference of temperatures when the the structureis erected and exposed temporarily to ambienttemperatures; consider both high and lowtemperature extremes

Design Loads During ConstructionStructural Analysis Load combinations may use strength design orallowable stress design Load combinations are not all inclusive Design should be based on the load combination(s)causing the most unfavorable effect ASCE 37-14 Standard is similar to ASCE 7-10 in thatwind loads have been reduced from 1.0W to 0.6W

Design Loads During ConstructionAllowable Stress Design – additive combinations

Design Loads During ConstructionLoad Combinations Using Strength Design

Design Loads During ConstructionExample Industrial Project, Support of hot tapmachine above existing pipe rack; Cp 4,900 lbsExisting pipe

Design Loads During ConstructionFailure during ConstructionUniversity of South Alabama, Mobile, ALIndoor Football Practice Facility collapse on July 22, 2017

Design Loads During ConstructionUniversity of South Alabama, Mobile, ALIndoor Football Practice Facility collapse on July 22, 2017No injuries or fatalities – Contractor was not working at the time of collapse

Design Loads During ConstructionConclusion on Report of Investigation of Collapse at University of South AlabamaNote that Building Collapsed at estimated wind speed of 46 mph

Design Loads During ConstructionHard Rock Hotel construction site in New Orleans Partialcollapse on 10/12/19 – 3 fatalities & several injured

Design Loads During ConstructionNumerous investigations are underway including OSHA;no final reports have been issued as of March 6, 2020Hard Rock hotel partial collapse – possible causes Insufficient shoring supports and/or removal ofshoring too early Change of metal form deck from initial design Not allowing enough time for concrete to cure Material defectsControlled implosion of remainder of building plannedfor April 2020 or later