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Concrete Slender Wall

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This program provides analysis of concrete wall panels that stand vertically and have applied vertical and out-of-plane lateral loads.

 

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The wall panel is analyzed using strength design procedures. Out-of-plane moments within the wall are created by eccentric axial loads, applied lateral loads, lateral self weight loads and moments induced due to the wall weight acting at an eccentricity when it deflects (P-Delta moments).

 

The ACI slender wall procedure, introduced in ACI 318-99, was first adopted by the IBC 2000 and subsequent code editions. As quoted in ACI 318R-05 Commentary, Section 14.8 is based on the corresponding requirements in 1997 UBC and experimental research presented in the 1982 "Test Report by SCCACI-SEAOSC".  Analytical study of the current IBC/ACI provisions for concrete wall panels showed the ACI procedure does not correspond to a bilinear load-deflection characteristic observed in the SEAOSC tests and significantly underestimates the service load deflection.

 

The ENERCALC Concrete Slender Wall program uses basic principles of structural mechanics to model the wall as a series of beam segments. For each segment the actual moment is used to calculate member stiffness using the Ieffective equations developed by Peter H. Bischoff. Since these changes to wall stiffness affect the wall deflection profile, the program performs an iterative analysis of calculating moments (including P-Delta effects).  The results are deflection curves almost exactly matching the SCCACI-SEAOSC test results. This makes this program far more accurate at calculating wall deflections and P-Delta effects than the simple equations in the ACI code.

 

 

Capabilities

This module provides these capabilities:

One or two story slender tilt-up concrete walls

Iterative process accounts for P-delta (12 iterations are used)

Optional parapet

Axial loads with optional eccentricities

Wind, seismic and user defined lateral loads creating bending on the wall panel

Variable strip width to model the wall panel

Temperature differential can be specified across thickness of wall to add curvature

Rebar location at center of wall or two layers of reinforcing at each side

Bottom of wall can be fixed or pinned for moment resistance

Top of wall can be pinned or free

A reveal can be defined and cross section properties modified for reduced thickness and optionally add rebar

The effects of wall openings can be addressed by modeling the solid panel between or adjacent to openings and then using superposition to apply the loads above and below openings.

 

 

General

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Material Properties

f'c

28-day compressive strength of the concrete.

 

Fy

Yield point stress of reinforcing

 

Ec

Modulus of elasticity of concrete. You can enter the value or click the

["57"] button to set Ec = 57000 * sqrt(f'c), or click the

["33"]  button to set Ec = 33 * sqrt(f'c) * ConcWeight1.5.

 

Fr: Rupture Modulus

Multiplier used in the expression to define the modulus of rupture for the concrete. 5.0 is the original recommended multiplier that was developed as a result of the SEAOSC slender wall tests of the early 1980s.  7.5 is the multiplier provided by ACI 318.

 

Concrete Wt

Weight of concrete in pounds per cubic foot.

 

Lambda

Factor to account for lightweight concrete.

 

Max Pu/Ag = f'c * <entry>

Enter a multiplier less than 1.0 which will be applied to f'c to determine the maximum allowable factored axial stress.

 

 

Thickness & Rebar

 

Wall Thickness

Total wall thickness

 

Bar Location

You can select bar placement at the center of the wall thickness or at each face. When selecting "Each Face" the module performs calculations considering both bars, unless the option is also selected to Ignore compression in rebar.

 

Rebar "d" Distance

Enter the distance between the outside surface of the wall to the centerline of the rebar. For bars each face this measurement can be from either face.

 

Wall Weight

The internally calculated wall weight considering the concrete weight and wall thickness entered.

 

Bar Size

Enter the US customary rebar size number.

 

Rebar [Spacing] / [# in Width]

These two options indicate how you will specify the rebar quantity in your design strip.

 

[Spacing] will change the entry so that you can enter a spacing in inches for the rebar.

 

[# in Width] changes the entry so you can enter the number of bars in your design strip, where the width of the design strip is entered on the Dimensions tab.

 

Note:  When using the "Each Face" option, the "# Bars in Width" specifies the number of bars on each face within the design strip width.

 

 

Analysis Settings

 

Ieff used for Deflection

The module offers the option to use Ieffective based on the moment in the individual wall elements or to use Icracked for the full height of the wall.

 

Temperature Differential across thickness

This input is used to describe the temperature change between each face of the wall. A temperature change induces a slight curvature into the wall because the hotter side expands, resulting in a slightly higher out-of-plane deflection.

 

Minimum Vertical Steel: %/100

Minimum steel as a percentage of the gross wall area.

 

Minimum Allowed (Span/Deflection) Ratio

This setting establishes the minimum allowable ratio of span length to service load deflection. If a lower actual Span/Deflection ratio occurs (meaning greater deflection), a warning message will be displayed.

 

Apply 0.75 Factor used in ACI Eq. 14-5 & 14-6

Please see the code reference for an explanation of this factor. It is typically not used in this module because it is a calibration factor used to curve fit deflection calculations with ACI approximate formulas.

 

Number of wall elements for FE solver to use

This module divides the wall design strip into segments from the base to the top for analysis purposes. Use this entry to define the number of segments to use. Experience demonstrates that approximately 30-40 segments gives a good balance between the iterative P-Delta analysis reaching convergence and excessive calculation time.

 

 

Dimensions

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Clear Height

Span of the wall between the base and the first lateral support. For one-story walls this is the top support. For 2-story walls this prompt will change to be "1st story height".

 

Parapet Height

Distance the wall extends above the topmost lateral support (i.e. extension above the clear height for one-story wall, extension above the 2nd story height for 2-story walls).

 

Wall Support Conditions

Controls how the top and bottom of the wall are restrained for moments and lateral movement.

 

 [Top & Bottom Pinned]

Base of wall is restrained against movement out of plane and vertically, rotates freely. Top of wall restrained against out of plane movement and can move vertically and rotate freely.

 

 [Top Pinned, Bottom Fixed]

Base of wall is restrained against movement about all three axes. Top of wall restrained against out of plane movement and can move vertically and rotate freely.

 

 [Top Free, Bottom Fixed]

Base of wall is restrained against movement about all three axes. Top of wall is completely free making this a cantilevered wall.

 

Reveal Data

A reveal is a portion of the wall that is recessed from the rest of the surface. It is formed by placing thin blockout material (typically styrofoam) in the forms prior to concrete placement. It is used to create architectural effects. The reveal reduces the structural thickness of the wall. This module calculates section properties for this reduced section in the portion of the wall where the reveal has been formed.

 

  Reveal Depth

Depth of reveal measured from outside face of wall. A 1" reveal in a 6" wall gives a net structural thickness of 5".

 

  Reveal Start Location, Reveal End Location

Distances measured upwards from bottom of wall that define the start and end points of the reveal.

 

Reveal Rebar

This selection defines how the module should consider the reveal area to be reinforced.

No Change means that the reinforcing stays where it is as defined by the "Rebar 'd' Distance" entered on the General tab. This option results in an offset rebar location within the remaining structural thickness, because the reveal takes away part of the concrete.

Drape Bars tells the module to move the rebar inward to give the same dimension between the rebar and face of wall. For walls with bars at "Center" this moves the bar to the center of the remaining structural thickness. When bars are specified on each face, this option moves only one of the bars inward.

Add Bars enables you to add additional reinforcing in the area of the reveal. The location of the main rebar is as described in the "No Change" option above.

 

Design Width of wall portion ("strip width")        

This module performs its analysis for this width. Results are for either this width or a 12" width as noted where the results are provided.

 

Note that applied loads either are applied to the entire strip width (as for concentrated vertical and lateral loads) or are entered on a per-foot basis when they are uniform loads.

 

Two Story...

When a two-story wall is selected, this tab changes slightly to provide the 2nd story height and remove the pure cantilevered support option.

 

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1st Story Height

Distance from the bottom of the wall to the first lateral support.

 

2nd Story Height

Distance from the first lateral support to the top lateral support.

 

 

Loads - Vertical

A variety of vertical loads are available. Note the hints describing whether the load is per foot or on the entire strip width.

 

All loads that are entered on this tab will be multiplied by the load factors specified on the Load Combination sub-tabs.  So these magnitudes should be specified with those load factors in mind.

 

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Ledger Load

This is a per-foot vertical load applied to the wall at an optional eccentricity. So if you have a 48" strip width and specify a 1 k/ft dead load then the strip will have a total of 4 kip applied due to the 1 k/ft entry.

 

 Eccentricity

Describes an offset from the mid-thickness of the wall panel, which is the default location of application of a vertical load. Enter this value as a positive number when the load is shifted toward the inside of the wall.

 

Concentric Load

This is a per-foot vertical load applied concentrically to the wall. So if you have a 48" strip width and specify a 1 k/ft dead load then the strip will have a total of 4 kip applied due to the 1 k/ft entry.

 

Mid-Height Vertical Uniform Load

This load entry is only shown for 2-story walls. It allows you to specify two uniform loads applied at the "1st Story" height, one of which can have an eccentricity from the wall center.

 

Concentrated Loads

These are single concentrated vertical loads applied to the wall "strip width" with an optional eccentricity.

 

Distance from Base is the height at which the load is applied.

 

Eccentricity describes an offset from the mid-thickness of the wall panel, which is the default location of application of a vertical load. Enter this value as a positive number when the load is shifted toward the inside of the wall.

 

 

Loads - Lateral

Lateral loads are applied perpendicular to the plane of the wall and are almost always seismic or wind. These loads create out of plane deflection of the wall, which the module will use to develop P-Delta effects to calculate secondary moments in the wall. Recall that this module divides the wall into small segments and calculates the allowable and actual forces and deflections for each small segment. In this way the lateral loads are properly modeled on what is effectively a beam with variable stiffness due to the state of cracking in each segment.

 

All loads that are entered on this tab will be multiplied by the load factors specified on the Load Combination sub-tabs.  So these magnitudes should be specified with those load factors in mind.  All lateral loads must be entered as positive values.

 

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Full area WIND Load

Enter the wind load that will be applied to the wall in the out-of-plane direction. This load will only be applied to one surface of the wall, and as such, the magnitude must take into consideration both the internal and external pressures.

 

Wall Weight SEISMIC Load

This section offers three options to specify the seismic load that will be applied to the wall in the out-of-plane direction:

 

Enter Lateral Load: This entry is a simple net load applied to the wall (but will still be factored by the load combination factors for "E").

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Enter Wall Weight Factor: Enter a number that will be multiplied by the self-weight of the wall. For example, if you enter 0.25 and the wall weighs 80 psf, then a 20.00 psf out-of-plane load will be calculated and applied to the wall using the load combination factors for "E".

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Enter SDS per ASCE-05: Enter the (SDS * I) value as prescribed by the ASCE code for the building location. The minimum calculated load value of 10 psf or (0.4 * Value Entered * Wall Weight) will be applied to the wall using the load combination factors for "E".

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Fp

This is the actual seismic load applied perpendicular to the plane of the wall, which represents the wall's seismic self weight load.

 

Concentrated Lateral Loads

This is an added lateral load applied perpendicular to the plane of the wall. It acts on the full "Strip Width" and is factored by the load combination factors corresponding to the type of load.

 

Distributed Lateral Loads

This is an added lateral uniform load applied out-of-plane to the wall. It acts on the full "Strip Width" and is factored by the load combination factors corresponding to the type of load.  You also enter the start and end distance of the load extent above the base of the wall.

 

 

Load Combinations

Typical load combination information as used throughout ENERCALC SEL.

 

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Summary

This tab presents the critical results as calculated by the module.

 

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Maximum Bending Stress Ratio

The module looks at the detailed results for ALL strength design load combinations at all "segments" in the wall and pulls out the maximum factored load bending stress ratio to present here as the governing condition.

 

Minimum Deflection Ratio

The module looks at the detailed results for ALL service load combinations at all "segments" in the wall and pulls out the minimum service load deflection ratio (meaning maximum deflection) to present here as the governing condition.

 

Moment Capacity Check

For the condition of maximum bending stress ratio, the actual applied and allowable bending moments are given along with the governing load combination.

 

Axial Load Check

The module checks the actual axial stress in all segments for all load combinations and gives the maximum actual stress Pu/Ag. The allowable value is the result of the user's entry for maximum percentage of f'c to use.

 

Service Deflection Check

For the condition of minimum deflection ratio (meaning maximum deflection) the ratio, deflection, allowable minimum ratio, allowable deflection (based on allowable ratio) and governing load combination are reported.

 

Reinforcing Limit Check

The module checks all portions of the wall for reinforcing (including differently reinforced first and second stories and reveal areas). It reports the maximum reinforcing ratio and compares it with the maximum percentage of balanced section analysis As allowed.

 

Minimum Moment Check

ACI specifies that a wall section in bending shall have a minimum strength phiMn that is greater than the cracking strength Mcr = Sgross * Fr.

 

Maximum Reactions

This gives a summary of the maximum reactions (both out-of-plane and vertical) along with the load combination that creates them.

 

 

Maximum Combinations

This tab provides a summary of the governing values for each load combination for both factored load axial & bending and service load deflections.

 

Factored Load Maximum Moments for Load Combinations: The module looks through the result set for each load combination and identifies the location above the base of the wall at which the maximum condition is found. Note that "Aseff" is the effective area of steel and is influenced by the axial compression in that segment.

 

Service Load Maximum Deflections for Load Combinations: The module looks through the result set for each load combination and identifies the location above the base of the wall at which the maximum out-of-plane deflection is found. The value for "Ieff" is specific to the segment at that location and is based on the actual moment and Bischoff's equation for calculating effective moment of inertia.

 

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Strength Design Results

This tab provides an extremely detailed summary of the factored axial load, moments, effective steel area and moment of inertia at each wall analysis segment for each load combination.

 

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Service Load Deflections

This tab provides an extremely detailed summary of the service axial load, moments, effective moment of inertia and calculated deflection at each wall analysis segment for each load combination.

 

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Reactions

This tab gives a summary of out-of-plane and vertical base reactions for each service load combination.

 

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2D Sketch

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Diagram

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3D Rendering

CSW 3D rendering

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