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The purpose of this survey is to provide the ASCE Task Committee on Drift Control of Steel Buildings with information that may be used to assess the state of the practice in designing steel buildings for wind. After the information is collected and analyzed, the committee will write a state-of-the-art report, which will be published in a major engineering journal or periodical.
Your participation in this study is completely voluntary. There are no foreseeable risks associated with this project. However, if you feel uncomfortable answering any questions, you can withdraw from the survey at any point. It is very important for us to learn your opinions in order to assess the State of the Art.
While the names of the firms filling out the survey will be recorded, this information will be held in confidence by the Task Committee, and will not be part of the published report.
The survey is divided into seven parts. It is recommended that respondents read through the entire survey before answering any of the questions.
Parts I through V of the survey relate primarily to issues related to wind drift. Part VI covers issues related exclusively to perception of motion issues
Part VII of the survey requires that the respondent perform drift related calculations for a hypothetical ten-story structure. The completion of this part of the survey is optional. To provide incentive for filling out this portion of the survey, one copy of SAP2000 or ETABS will be awarded to one of the firms that fully completes this part of the survey. The firm designated to receive the software will be determined by a drawing.
Your survey responses will be strictly confidential and data from this research will be reported only in the aggregate. Your information will be coded and will remain confidential. If you have questions at any time about the survey or the procedures, you may contact Dan Berding at the email address specified below.
Thank you very much for your time and support. Please start the survey now by clicking on the Continue button below.
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| Your location (City and State): | | |
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Your level of college education:
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| Number of years of professional experience: | | |
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Employee Education and Experience |
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| Total number of structural engineers in your firm who design buildings (including all offices): | | |
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| Average years of college education for individuals performing structural analysis and design calculations related to this questionnaire: | | |
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| Average number of years of professional experience of persons performing calculations related to this questionnaire: | | |
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| Average number of years of professional experience of persons in responsible charge of persons performing calculations related to this survey: | | |
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Which Design Philosophy does your firm employ with respect to steel structures? (answer in percent so that the total sums to 100)
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| Complete the following table that indicates the volume of work in your firm over the last ten years. Please enter the approximate number of steel buildings in the specified building use category. If your firm has been designing buildings for less than ten years, specify the appropriate number of years in the space provided below the table. |
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Number of Steel Buildings Designed over the Last 10 Years
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| Number of years designing buildings if less than ten years: | | |
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What software does your firm use with respect to lateral load analysis for steel structures? List the three programs most often used for each building height category. Enter “in-house” if the software was developed by your firm:
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II.) Wind Drift: General Issues
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| Is wind drift a common design issue for buildings designed by your firm? |
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| Does your firm have written policies and procedures related to wind drift? |
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| If you have written policies and guidelines, would you be willing to share them with the Task Committee? |
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Why do you limit drift? Please rank the following reasons in terms of priority 1 to 5 with 1 being the highest priority.
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| Please discuss any other reasons you have to limit drift. | | |
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| Current building codes (e.g. 2005 IBC) do not specify drift limits for wind loads. Do you believe that standards should be developed for wind drift? |
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| Please explain your answer. | | |
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Complete the table below for the five structural steel buildings that were most recently designed by your firm in which wind controlled the design of lateral load system (seismic controlled ineligible). Under “Wind Design Controlled by” indicate which single item predominately controlled the size of the lateral load resisting members.
* Frame type: Moment Frame w/ Rigid Connections (MFR), Moment Frame w/ Flexible Connections (MFF), Braced Frame (BF), Combined System (CS), Other (O).
*Use: Commercial (C), Residential (R), Industrial (I), Institutional (I), Other (O).
*Terrain: Urban (U), Suburban (S), Coastal (C).
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Indicate which single item predominantly controlled the design of the lateral load resisting system for the buildings described above.
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III.) Structural Modeling Issues
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| When modeling buildings, the structure is most often modeled... |
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When modeling in three dimensions, a variety of floor diaphragm models may be used. How often do you use the approaches listed below? |
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| Briefly explain your answers to the previous question concerning floor diaphragms. | | |
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When modeling beams and girders, do you explicitly consider the following effects?
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When modeling columns, do you explicitly include the following effects?
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When modeling diagonal braces, do you explicitly include the following effects?
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Do you explicitly include beam-column (panel zone) deformations?
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When modeling the beam column joint (panel zone) region of moment resisting frames, a variety of approaches may be used. Indicate how often the following models are used.
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| When beam-column joints are modeled explicitly, the following model is most often used: (Check one) |
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Do you design structures with semi-rigid (partially restrained) connections?
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Do you explicitly include non-structural elements in the model?
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Do you include foundation flexibility in your analytical model?
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Do you include second-order (p-delta) effects?
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When modeling P-Delta effects, please indicate how often the following procedures are used.
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| When including P-Delta effects, what percent of TOTAL UNFACTORED live load do you consider when computing story gravity loads? | | |
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| Do you use any procedures for optimum (least weight) distribution of materials? |
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| Moment Resisting Frames | | | | Partial Rigid Frames | | | | Braced Frames | | |
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| Where do you obtain wind loads for steel buildings?(answer in percent so that total sums to 100) |
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| Do you use different wind loads for serviceability and strength? |
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| What return period (years) do you use for wind drift? | | |
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Does the owner or architect play a role in deciding what MRI to use for serviceability?
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| When designing for strength, ASCE-7 requires the consideration of eccentric wind loads. Do you use eccentric wind loads when evaluating drift? |
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| Do you believe the code procedures for determining wind loads are clear? For example, would two engineers working independently calculate the same wind loads for a given structure, location and wind return interval? |
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| What is the primary motivation for recommending the use of a wind tunnel? |
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| For what building height do you generally recommend wind tunnel tests? |
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| When using a wind-tunnel, do you use different terrain models for drift and strength issues? |
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| When using code based loads, do you use different terrain models for drift and strength issues? |
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| Are you familiar with Database Assisted Design? |
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| Have you used Database Assisted Design? |
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| Which of the following measures of drift is most often used in your firm? |
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| At what location in the floor plates do you compute the drift? |
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When comparing the allowable wind drift to the quantity computed in the previous two questions, the allowable drift is a function of the following: (Indicate importance for each item, using a scale of 1 to 5, where, 1 is least important and 5 is most important)
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| Have you ever performed an analysis to determine whether it is more economical to add stiffness to avoid damage, or to accept damage and the associated costs? |
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Example Buildings
Four hypothetical building are to be designed by your firm. On the basis of your current design procedures, fill in the last three columns of the table below each building description. Enter the drift limits as a ratio (e.g. H/500 would be entered as 0.0020). If you use strain as a drift measure, enter the strain directly. |
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Building 1: A one story warehouse with moment resisting frames, metal cladding and no interior partions.
Building 2: A 10 story hospital with braced frames, brick cladding and interior partitions of drywall.
Building 3: A 30 story office building with moment resisting frames, glass and granite curtain wall and drywall partitions (in the service core only).
Building 4: An 80 story framed tube hotel with a glass curtain wall and drywall partions (in the service core only).
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VI.) Perception of Motion (optional)
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This portion of the survey is optional. Please respond only if you have significant experience in designing buildings where perception of motion due to wind is a common design issue. |
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| Which factors are most likely to cause perception of motion to become a design issue?(Select all that apply) |
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| Does your firm have written policies and procedures related to perception of motion? |
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| Would you be willing to share the guidelines with the Task Committee? |
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| What wind mean recurrence interval (years) do you use for perception of motion? | | |
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| Moment Resisting Frames | | | | Partially Rigid Frames | | | | Braced Frames | | |
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What motion limits (in milli-g) do you use for the building types indicated below. The motion limit should correlate with the MRI selected in question 5. Please indicate if the motion limits are maximum or RMS. |
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| Office Buildings | | | | Residential Buildings | | | | Mixed-Use Facilities | | |
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| Are the motion limits specified frequency dependent? |
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| Are the motion limits specified part of a standard (e.g. ISO). If so, please specify. |
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| Do you use approximate formulas for estimating motion in tall buildings? If so, please provide a reference below. (Example: National Building Code of Canada) |
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Please fill in the following two tables below with respect to perception of motion issues in the past five steel building you designed where motion was a design issue.
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| Have you ever used any of the following motion control devices in the design of your buildings? (Check all that apply) |
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| Have you ever taken a “wait and see” approach to the use of controlling devices, where a building is completed without the device, and such devices are implemented only after building use indicates that such devices are necessary? |
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| Have you ever taken an "informational approach" to the problem of wind induced motion (i.e. inform the owner/occupants that the building is safe and the motion is to be expected on occasion)? |
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| Current building codes (e.g. 2005 IBC) do not specify lateral acceleration limits. Do you believe that standards should be developed for such limits? |
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| Please explain your answer. | | |
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VII.) Structure Calculations (Optional)
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In this part of the survey you are asked to perform calculations related to the structure shown in Figure 1.
The lateral load system for this ten-story building consists of moment resisting frames in the N-S direction, and X-Braced frames in the E-W direction.
The building is located in Jersey City, NJ. An aerial photograph of the terrain surrounding the building is shown in Figure 2.
The building is used for general office space. Drywall is present around the interior core only. Tenants may build out office space as required for their needs. Cladding consists of a glass/granite curtain wall.
Elevations of the frames are shown in Figure 3. Beam, column, and brace sizes are provided. All connections in the moment frame are fully welded. Connections in the braced frame are field bolted. Typical details are shown in Figure 4.
For this exercise, assume that the floor diaphragms are rigid in-plane, and have no stiffness out-of-plane. For the moment frame, assume that columns are fixed at the base. For the braced frames, assume that the columns are pinned at the base.
When performing the structural analysis, it is very important that the building be analyzed in conformance with the current state of the practice in your firm. Please do not modify your calculation on the basis of what you infer from the questions asked in this survey. Do not check the building for strength.
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PART 1
Assume that a 100 kip load is applied at each floor level, including the roof. Determine the total lateral displacements at each level of the building for the loads applied in the N-S direction and in the E-W direction, done independently. Enter the results in the following table.
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PART 2
Using ASCE 7-05 to determine wind loads, perform a structural analysis, and complete the tables below.
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For Winds Blowing in the N-S Direction
*Drift calculated at CENTER OF MASS
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For Winds Blowing in the E-W Direction
*Drift calculated at CENTER OF MASS
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| Please write a short (500 words or less) description of your analysis. This description should be written in the context of the questions asked in this survey (did you include shear deformation, p-delta effects, and so on). | | |
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| Please use the space below to provide any additional information or comments about the survey. Thank you! | | |
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