Design Loads on Structures during Construction

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Although these loads are combined struction being considered; L is the live load, which with dead loads in the design load combination, it may may be less than or greater than the final live load; and be highly unlikely that multiple independent variable W is the wind load computed using the design velocity loads will reach maximum values at the same time.

Accordingly, some reduction in the total combined The most unfavorable effects from both wind and load effect may be justified. However, the designer is earthquake loads shall be considered where appropri- cautioned that when correlated variable loads are con- ate, but they need not be considered simultaneously. Other construction loads that shall be considered if applicable are defined in Section 2. The base shear caused by lat- eral forces wind or flood shall not exceed two thirds of the total resisting force caused by friction and adhe-.

ASCE The de- under consideration. The dead load includes all con- sign of temporary shoring and bracing must include struction in place that is temporarily shored or braced.

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It includes construction for which the primary struc- scribed in Sections 3, 4, 5, and 6, as applicable. The weights of scaffolding, shoring, concrete ous engineering handbooks. The weight of the permanent construction that is in place includes all nonstructural loads such as cladding, partitions, ceilings, railings, and so on that are expected to be in place at the particular time being considered. The live load, L, may vary at different ent than the live loads applied on the completed struc- stages of construction. For example, during reconstruction of a bridge For bridge structures and other transportation designed for trucks, a lane may be restricted to cars, re- structures, live load shall include impact, longitudinal sulting in a lower live load.

On the other hand, tempo- forces from vehicles, centrifugal forces from vehicles, rary overcrowding of a completed section of a building and wind loads on vehicles, as applicable. Reduction of the live load from the final design value shall not be made unless the use of the facility is strictly monitored and enforced.

The partially completed structure, or partially de- molished structure, should expose the occupants or users to no greater risk than inherent in the codes and standards of practice that pertain to the completed structure. Ideally, the design drawings will identify live loads to be applied during construction, if applicable. These loads are to be com- sures of earth. Stairs, ladders, and elevators are not addressed in this standard.

Construction loads include, but are not limited to, materials, person- nel, and equipment imposed on the temporary or per- manent structure during the construction process. Construction dead load, CD: the dead load of temporary structures that are in place at the stage of construction being considered.

The dead load of the permanent structure, either partially complete or com- plete, is not included in CD; the dead load of the per- manent structure is defined as dead load, D, in Section 3. Individual personnel load: a concentrated load of lb 1. Working surfaces: floors, decks, or platforms of temporary or partially completed structures which are or are expected to be subjected to construction loads during construction.

Material Loads C4. Material Loads The material dead loads consist of two categories: This section separates material dead loads into two categories: FML and VML, which are separated to per- 1. This approach recognizes the The FML is the load from materials that is fixed in difference in the variability of the load between the magnitude. The VML is the load from materials that two categories. If This section addresses the loads from materials the local magnitude of a material load varies during the and is not intended to apply to equipment loads. Material loads may be either distributed or con- centrated loads.

The designer must determine whether the superim- Downloaded from ascelibrary. For example, the load from formwork becomes a FML once it is in- stalled, and the load created by the concrete during fresh concrete placement is considered a VML. The load caused by concrete placement is considered a VML because fresh concrete can be piled higher than the finished thickness of the slab. The distinction between a FML and a VML is not location or position on the structure; rather, it is the variability of the loading magnitude. The stockpiling of any material is considered a VML scaffold, forms, rebar, metal deck, barrels, dry- wall, ceiling tile, roofing materials, and so on.

Some materials, such as scaffold or forms, are considered VMLs when they are stockpiled but may be considered FMLs when they are placed in their final end use posi- tion. Engineering judgment must be used to determine whether the stockpiled material should be considered a uniformly distributed or a concentrated load. Stockpiled materials should be positioned on the structure to minimize the effects of early loading on the serviceability or performance of the completed structure.

Careful consideration should be given to the placement of stockpiled materials on early-age con- crete structures. Early loading of low-strength concrete has been shown to increase long-term deflection Fu and Gardner ; Sbarounis ; Yamamoto It is recommended that materials be stockpiled at columns, avoiding placement in the middle of long spans. This practice serves to decrease long-term de- flections of reinforced concrete beams and to deter lat- eral buckling of unsupported steel beams. For a list of the proper weights for different build- ing materials, the designer should consult ASCE or other specified or recognized sources.

When the con- crete gains sufficient strength so that the formwork,. Once such materials have been discharged from Section 4. The personnel and equipment loads used in the de- sign or analysis of a partially completed or temporary structure shall be the maximum loads that are likely to be created during the sequence of construction. However, design for that would result from the application of concentrated equivalent uniformly distributed loads is a long-stand- loads that could occur and are not separately consid- ing practice that has stood the test of time.

The de- ered. Section 4. The type of equipment to be used for each conditions in the structural members. The designer construction operation, its location on or off the struc- shall consider each category of minimum concentrated ture , and its loading must be considered. Loads for personnel and equipment load that is likely to occur different types of construction equipment have been during the construction process.

See also Concentrated loads from equipment shall be deter- Sections C4. For temporary structures that are used for public Individual personnel load, defined in Section traffic, the structure shall be designed in accordance 4. Area of Load Wheeled vehicles, both manually operated and Minimum Application powered, may require a more rigorous analysis similar Loada in. Wheel of manually 2. Need not be less than 18 in. In some instances, the authority with jurisdiction may require that provisions be made for specified con- centrated load.

Examples of materials that might be covered are piles of unspecified debris and pallets of with the AASHTO bridge design specifications material. If the source of the concen- trated load can be clearly identified, such as wheel loads, axle loads, pallet loads, or equipment reactions, that specific load should be distributed as determined by its source. Problems arise in determining the distribution ar- eas of unidentified, but specified, loads. To determine the distribution area for an unidentified concentrated load, assume that the load will be generated by the densest material normally available on a construction site.

That material is arbitrarily chosen to be concrete at pcf This should provide the smallest distribution area for a pal- let load or a pile of material generating the concen- trated load. The specified concentrated load in Table 1 is as- sumed to be the total load, including dynamic forces. The concentrated loads required herein are not in- tended for protection against an accident involving falling objects, such as when a beam, a length of rein- forcing steel, or a piece of equipment falls several sto- ries.

Provision shall be made in the structural design charged from a bucket from excessive heights above. A concrete bucket that hits the forms is impact forces. Said force shall zontal loading. Also, horizontal loads can be created be applied in any direction of possible travel, at the from personnel and equipment operations. The designer should be aware that the actual hori- 2. For equipment reactions as described in Section 4. This load shall be ap- force that could be generated from the activities of per- plied in any direction and shall be spatially dis- sonnel. This load need Criterion 4 is intended to provide a minimum lat- not be applied concurrently with wind or seismic eral load resistance and to assure lateral stability for load.

Generally, This provision shall not be considered a substitute it is not expected that this criterion will result in forces for the analysis of environmental loads. Wind and other phenomena that produce horizon- tal loads must be considered separately from the re- quirements of this section, except as permitted for cri- terion 4. C Inter- nal Cable Bracing Systems. This revision to their pre- viously issued document appears to address many of the erection forces normally encountered, such as fit- ting, aligning, and bracing operations, that are nor- mally performed with the help of guys.

For sign of the temporary or partially completed structure. Examples of calculations for re- of the equipment operating at its maximum rated load actions from lifting or hoisting equipment that include in conjunction with any applicable environmental assessments of environmental loads are provided in loads, unless the use is restricted and revised reactions Shapiro et al.

The design brid situations such as the use of a crane with rear out- shall include the consideration of support deflections riggers placed over a major support member of the or movements, out-of-level supports, vertical misalign- structure. At this point, the crane may reach out to its ment, and environmental loads on the equipment. In this case, maximum out- rigger loads are apparently developed over the rear of the crane and lesser loads are developed over the other outrigger pads, which could be placed on lighter struc- tural members.

This is a common practice when the outrigger support members are not adequate to sustain the full or maximum rated capacity outrigger reactions.

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Because of a shift of the center of gravity, vehicle axle loads and crane outrigger or support reactions may be greatest in the absence of payload or pick. The worst case condition controls loaded or unloaded. Axle load dis- Unless loaders, such as front end loaders or fork- tributions at maximum load do assume that all of the lifts, are intentionally restricted from tipping on one axles are touching the ground and with a certain load axle, the loader selfweight plus tipping load shall be distribution.

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Unless special precautions are taken, such applied to the front axle. If the basis of the rating is different than the con- element of the deck or try to pick more than their rated ditions under which the equipment will be used, the load. In this instance, the entire vehicle picks up and more severe reactions shall be used in design. Equation assumes a pressure of the newly placed concrete given by Equa- fully liquid head and normally can be applied without tion Maximum and minimum values given for restriction.

However, there are exceptions. Caution other pressure formulas do not apply to Equation For columns or other forms that may be filled The SI version of the lateral pressure formula is rapidly before any stiffening of the concrete takes adopted from ACI R ACI ; Hurd place, h shall be taken as the full height of the form or and from the Appendix of ACI R In certain in- stances, pressures may be as high as the face pressure of the pump piston.

When shoring is continuous over several floors, the calculated loads on these shores shall be cumulative unless and until the shores have been released and reset to allow the slab in question to carry its own dead weight. Such release should not oc- cur until the concrete is capable of carrying its own dead load. This sec- tion includes rules for applying and combining the var- ious loads, as well as traditional minimums for several common construction processes.

The design construction load shall include the crit- The combination of the various forms of construc- ical combination of personnel, equipment, and material tion loads, materials, personnel, and equipment is an loads. Structures supporting work- C4. It is traditional to design ing surfaces as defined in Section 4. When the construction operation fits the definition Temporary structures have often been designed, in Table 2, the designer is permitted to design for the advertised, and specified by the light, medium, and tabulated uniform loads as the vertical load from the heavy duty ratings given in Table 2.

This standard also combination of personnel, equipment, and material in applies to partially completed structures, and the same transit or staging. When the construction operation terminology is adopted. Different styles of construction does not fit the definitions in Table 2, the design shall and different segments of the construction industry be for the actual loads. Concentrated loads shall be have different traditions for design loads on partially considered separately. Following are examples of working surfaces that Downloaded from ascelibrary.

Construction Live Load!

Attics or hung ceilings that provide access for maintenance, installation of utilities, and emergency services such as firefighters. These working surfaces must be addressed in ac- cordance with Sections 4. When C4. This temporary structures are specified by load name, the requirement will encourage uniformity in terminology names of the load class and the magnitude of design for capacity of scaffolds and similar structures.

Checkerboard loadings on floors and mul- effect than the same intensity applied over the full tistory frames produce the highest positive and length of the structure or member. Cantilevers cannot rely on a possi- ble construction load on the anchor span for equilib- rium. ASCE describes other possible conditions of designing members or floors for partial loading. No reduction is allowed for fixed or variable material loads, except to the extent that small amounts of material in transit or staging are included in uniformly distributed personnel, equip- ment, and material loads, such as those in Table 2.

When justi- C4. Uniformly fied by an analysis of the construction operations, distributed loads are a convenient substitute for com- members having an influence area of ft2 puting the combined effect of several concentrated As such they are generally calibrated to a partic- formly distributed personnel and equipment load deter- ular area. For smaller areas, the concentrated loads mined by applying the following formula: control structural design.

There is a lack of data from construc- area supported by the member; Lo is the unreduced tion projects. Without specific information, the uniformly distributed personnel and equipment design derivation of a new reduction equation was not war- load per ft2 m2 of area supported by the member; and ranted. Therefore, a commonly used live load reduc- AI is the influence area, ft2 m2. The influence area AI tion procedure ASCE has been used for this is normally four times the tributary area for a column, document. If actual loads are The reduced uniformly distributed personnel and anticipated over the entire area, no reduction should be equipment design load, regardless of influence area, taken.

Model building codes have the tributed personnel and equipment load is 25 psf 1. A reduction in gravity construction loads for per- Roofs. For consistency, the reduction in roof personnel sonnel and equipment on a roof is also permitted based and equipment loads also follows ASCE The de- upon the slope of the roof. The reduction factor R is: tail of application is somewhat different, but the limits are essentially the same. R need not exceed 1. This issue should not be confused with 1. Scaffolds with working surfaces of 40 ft2 3.

Load reduction, based on influence area, is sonnel loads that they can support, and the working addressed in Section 4. When design- The posting or load restriction can be accom- ing, the individual personnel loads shall be placed in plished by physical barriers that direct the traffic on a such locations as to maximize their effects on the bridge deck or parking structure, or barriers on a floor structural members of the scaffold; however, they system to restrict access to wheeled vehicles, storage need not be spaced closer than 2 ft 0.

Working surfaces designed for superimposed uni- It is not uncommon to have relatively large work form loads of 25 psf 1. These work- bridge. As a platform for personnel and equipment, ing surfaces shall be restricted accordingly. Working surfaces designed for loads less than what priate to design the deck system. However, recogniz- could reasonably be expected to be placed thereon ing that the work crew may consist of several person- Downloaded from ascelibrary. The hanger or support system for the platform could be designed for the maximum load developed by the limited number of personnel on the platform clustering around one sup- port to create the greatest load at that support point.

The platform would be clearly posted or rated, as with scaffolds in accordance with the ANSI maxi- mum number of occupants. Failure to do this could result in a loading on the structure from which the scaffold is hanging or supported, substantially exceed- ing the design load of that structure. There are many lightweight platforms and scaf- folds that are intended to support only one to three per- sons, their small tools, and incidental materials. The capacities of these scaffolds are controlled by the number of individual personnel loads for which they are designed.

Restriction of use is necessary to prevent overloading. Caterpillar performance handbook, Caterpillar, Inc. Fu, H. Francis Young, ed, American Concrete formwork for concrete. Institute, , Detroit. Hurd, M. New York. Jahren, C. California false- New York. Sbarounis, J. Concrete Int. Gardner, N. The following technical documents are readily obtain- T. Ratay, ed. Steel structures. Prentice- tion M4, , Chicago. Hall, , New York. Lowrise sign specification for structural steel buildings, Section building systems manual, , Cleveland, OH.

M4, , Chicago.

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Steel structures—de- structural timber framing. Yura, J. Sections other than those referenced here may able braced, Lehigh University Press, , Bethle- also apply. Their neering practice. One test of credibility of a method of determination for design should be performed by an earth pressure determination shall be its publication in engineer with adequate knowledge of soil mechanics, one or more generally accepted references on geotech- understanding of structural behavior, and familiarity nical engineering. Site-specific conditions shall be considered in the Innovative methods of temporary excavation sup- selection of method s of calculation, and site-specific ports are continually developing.

Construction Live Load! - Structural engineering general discussion - Eng-Tips

The application of data shall be used for the critical factors in the calcula- existing methods of earth pressure analyses should be tions. Laboratory or field instrumentation, observations, and measurements shall be permissible bases for deter- mination of earth pressures. Canadian Foun- dation Engineering Manual, 3rd Ed. Gordon, M. Sacramento, Calif. The basic reference for computation of environ- This section deals with special issues of construc- mental loads is the edition of ASCE 7.

The re- tion and temporary structures for which the basic pro- quirements of ASCE shall be applied except as cedures of ASCE are to be modified. The objective of this standard is to provide a level When an environmental loading is contained in of safety during construction that is comparable to that another document acceptable to the authority having of the completed structure. To achieve this, the proba- Downloaded from ascelibrary. Standards and other documents applicable to spe- cific materials or methods of construction have been de- veloped and are recognized and used extensively e.

During construction, the primary oc- cupancy of a building is by construction personnel. Design wind pressures shall be based on design Information and guidance have been lacking in the velocities calculated in accordance with Section 6. Limited research and development have been performed for the purpose of this standard Boggs and Peterka ; Rosowsky If local conditions so dictate, and for certain haz- ardous construction operations, it might be appropriate to apply a minimum wind pressure, such as 10 psf 0.

The reduced construction period velocity fac- 1 to 2 years 0. Local wind speed data should be consulted when using these factors. The construction period C6. The dates selected to shall be taken as the time interval from first erection to represent the hurricane season are not intended to in- Downloaded from ascelibrary. The dates system, including installation of cladding. For continuous work C6. During erection, periods, it shall be permissible to use wind speeds many structural components, including columns, gird- lower than those specified in Section 6.

For continu- ers, trusses, formwork, and facade panels cannot be ous work periods, the basic wind speed shall be not made to meet the requirements for the construction pe- less than the predicted speed, adjusted to the 3-second riod because they are being lifted or they have not been gust speed, as reported by the National Weather Ser- fully incorporated into braced and secured structures.

Continuous work periods end at the and so on should be employed as necessary for contin- end of the work day, at which time the structure shall uous work periods. At no time should wind speeds be made inherently stable, or appropriately secured, to used for continuous work periods exceed those recom- meet the requirements for the construction period as mended by manufacturers of equipment used in the defined in Section 6.

Weather forecasters sometimes publish predicted wind speeds based on different sampling periods.

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The sampling period must be known, and the predicted wind speed must be adjusted to be consistent with pro- visions of ASCE For the purposes of this Stan- dard, to obtain 3-second gust speeds multiply fastest- mile or 1-minute average speeds by 1. At the end of continuous work periods, when the duration of the operation exceeds the time period. Certain rigging operations may, by their very na- ture, pose hazards, and may require more restrictive measures to conform to ordinance of the authority hav- Downloaded from ascelibrary. An example is to provide free-fall areas for the materials being handled, which may result in closure of streets or sidewalks, or evacuation of buildings.

Unless de- more surfaces and often with higher drag coefficients tailed analyses are performed to show that lower loads than in the fully enclosed structure. For common ar- may be used, no allowance shall be given for shielding rangements of elements in typical open frames and of successive rows or towers. Con- For unenclosed frames and structural elements, sidering the changing nature of the building silhouette wind loads shall be calculated for each element. Unless and the arrangement of construction materials on the detailed analyses are performed, load reductions structure, it is prudent to assume that loads will not be caused by shielding of elements in such structures with reduced because of shielding, except in certain specific repetitive patterns of elements shall be as follows: cases.

For open structures with regular patterns of ele- 1. The loads on the first three rows of elements along ments, the direction of maximum force on the structure the direction parallel to the wind shall not be re- usually is not parallel to the principal axis of the struc- duced for shielding. Shielding effects are minimized, and therefore 2. Wind load al- wind is not parallel to the column lines.

For this rea- lowances shall be calculated for all exposed interior son, the most severe loads on an open structure include partitions, walls, temporary enclosures, signs, con- components of load in both principal directions of the struction materials, and equipment on or supported structure. These loads shall be added to the Shapiro et al.

The design velocity shall be factored upward creased and wind directions are altered. In general, from the basic velocity by the square root of the suc- pressure and suction coefficients will be higher than at tion coefficient for cladding as given in ASCE Also, there may The calculated wind velocity shall be used with appro- be substantial side and uplift loads on nearby adjacent.


At structures such as scaffolding in these locations. Spe- building corners, the resulting pressures shall be as- cial attention should be given to the loads on staging sumed to act on adjacent staging structures in horizon- structures near the edges of enclosed and partially en- tal directions parallel to and perpendicular to the enclo- closed structures. At top edges of enclosures, pressures Guidance for pressures on edge regions of sur- shall be assumed to act upward as well as horizontally. Thermal lag of struc- lowing temperatures for the months when the tural elements is considered by specifying that calcula- portion of the structure is erected and exposed tions be based on highest mean daily maximum and temporarily to ambient temperatures lowest mean daily minimum temperatures for the i the highest mean daily maximum tempera- months when the structure is exposed to ambient tem- ture and the lowest mean daily minimum peratures.

Additional highest mean daily maximum temperature, temperature data are also available NAS ; Na- or tional Climatic Data Center When portions of the structure that will be shielded forces in those components and attachments without when the structure is completed are subjected to di- serious consequences. However, if the attachments are rect solar radiation during hot weather, or rigid, extremely large forces may develop because of 3.

When temperature changes create distortions that the restraint of movement. Damage occurs when could damage structural or architectural compo- stressed elements are incapable of supporting the re- nents. Although damage is possible in almost any build- ing, buildings that are most susceptible are those that have relatively unrestrained frames supporting rigid el- ements, such as precast panels or masonry infilling walls, that are not a part of the primary structural sys- tem Martin Long buildings, in which the cu- mulative dimensional changes can be large, and build- ings erected during the extremes of the construction season, when ambient temperatures can be very differ- ent from end-use temperature, are particularly suscepti- ble.

Also, structures with braced bays or shear walls in. Multistory buildings usually show the most dam- age in the lowest stories, where the foundation pro- vides the greatest restraint to free movement ACI Solar radiation on a large surface during construc- Downloaded from ascelibrary. This can overstress a component that is designed to be shielded in the fin- ished structure. Thermal distortions are often impossible to re- strain because the forces that are generated exceed the capacities of practical restraining elements. Therefore, it is advisable to accommodate distortions by se- quencing the erection so as to avoid making rigid connections between portions of the structure that may undergo differential movement until the tempera- ture of the frame can be stabilized, or by installing structural and architectural details that will tolerate movement.

If construction will not occur during win- ter months when snow is to be expected, snow loads need not be considered, provided that the design is re- viewed and modified, as appropriate, to account for snow loads if the construction period shifts to include winter months. Design for snow loads that are lower than those described in this section shall be permissible, provided adequate procedures and means are employed to re- move snow before it accumulates to levels that exceed the loads used for design.

Should Temporary Structures be Designed with Higher Allowable Stresses?

How- ever, it should also be realized that loads in excess of statistically determined design loads may occur. If a range of conditions will exist during struction. These conditions may be quite different from construction, a series of load calculations shall be those that will exist once the building is occupied. The slope factor, Cs, shall be deter- vided in a building, and most buildings under construc- mined based on the construction-phase values of Ct tion are unheated, snow loads may be higher during Downloaded from ascelibrary.

The roof is also a dead load. Dead loads are also known as permanent or static loads. Building materials are not dead loads until constructed in permanent position. Live loads, or imposed loads, are temporary, of short duration, or a moving load. These dynamic loads may involve considerations such as impact , momentum , vibration , slosh dynamics of fluids and material fatigue. Live loads, sometimes also referred to as probabilistic loads, include all the forces that are variable within the object's normal operation cycle not including construction or environmental loads.

Roof and floor live loads are produced during maintenance by workers, equipment and materials, and during the life of the structure by movable objects, such as planters and people. Environmental Loads are structural loads caused by natural forces such as wind, rain, snow, earthquake or extreme temperatures. A load combination results when more than one load type acts on the structure.

Building codes usually specify a variety of load combinations together with load factors weightings for each load type in order to ensure the safety of the structure under different maximum expected loading scenarios. For example, in designing a staircase , a dead load factor may be 1. These two "factored loads" are combined added to determine the "required strength" of the staircase. The reason for the disparity between factors for dead load and live load, and thus the reason the loads are initially categorized as dead or live is because while it is not unreasonable to expect a large number of people ascending the staircase at once, it is less likely that the structure will experience much change in its permanent load.

For aircraft, loading is divided into two major categories: limit loads and ultimate loads. Ultimate loads are the limit loads times a factor of 1. Crash loads are loosely bounded by the ability of structures to survive the deceleration of a major ground impact. Loads on the ground can be from adverse braking or maneuvering during taxiing. Aircraft are constantly subjected to cyclic loading. These cyclic loads can cause metal fatigue. From Wikipedia, the free encyclopedia.

American Society of Civil Engineers. Eurocode 0: Basis of structural design EN Bruxelles: European Committee for Standardization. Mark's Standard Handbook for Mechanical Engineers 10th ed. International Building Code. Reliability Based Design.