Design Criteria
Project Information
Input | Description |
|---|---|
Project | Project name |
Location | Location of the project |
Date | Date printed on the report (defaults to current date) |
Client | Name of the client |
Designer | Name of the designer |
Job Number | Job number for the project |
Design Number | Design number for the design |
PCI Edition | Edition of the PCI Design Handbook to use |
Description | Long form description for the project. Shift+Enter adds a new line. |
Material Properties
Precast / Topping Concrete
Input | Description |
|---|---|
f’c | Final compressive strength of the beam concrete (often referred to as the 28-day strength). |
f’ci | Concrete compressive strength at time of release of the prestress in the casting yard, or at time of stripping of members without prestressing. The release strength cannot exceed the final compressive strength. This is used for all stripping and handling analysis. It may also be used for erection (user input). |
f’ct | Final compressive strength of the topping concrete (often referred to as the 28-day strength). |
wc | Density of the concrete used in the beam. |
Ec | Modulus of elasticity of the beam concrete at final. This value will be calculated and updated when f’c or the unit weight of the beam are changed. |
Eci | Modulus of elasticity at time of release of the prestress in the casting yard, or at time of stripping of members without prestressing. This value will be calculated and updated when f’ci or unit weight are changed. |
Ect | Modulus of elasticity of the topping concrete at final. This value will be calculated and updated when f’ct or the unit weight of the topping are changed. |
Type | Beam concrete type can be designated as normalweight, sand-lightweight, or all lightweight. |
λ | User options for either a user defined light weight concrete factor or an automatically computed one. |
Stress Stain Curve
The concrete stress strain curve comes from Collins, Michael P. and Mitchell, Denis, Prestressed Concrete Structures. This curve is used anytime the stress strain curve needs to be evaluated for the concrete, which can happen for flexure capacity.
Rebar / Transverse / Mesh
Input | Description |
|---|---|
fy | Yield strength of the rebar / wire. Note that rebar can (and usually does) have a different yield than wires. |
Es | Modulus of elasticity of the rebar / wire. |
Stress Strain Curve
The mild stress strain curve assumes linear elastic behavior up until yield. At that point the stress always returns the yield stress. Strain hardening is not accounted for and rupture strain is not checked.
Strand
Input | Description |
|---|---|
fpu | Ultimate tensile strength of prestressing steel. |
Ep | Modulus of elasticity of prestressed reinforcement. |
Stress Strain Curve
The prestress stress strain curve uses the equations found in the PCI Design Handbook 8th Edition Design Aid 15.2.3. Note that in these equations, the coefficients found in the equation are solved for to account for the user defined material properties. The yield stress in the strand is assumed to be 90% of the ultimate stress.
Prestress Losses
Input | Description |
|---|---|
Method | Losses can be user defined, calculated using the lump sum method present in the PCI Design Handbook, or calculated using the time dependent method in the PCI Journal. |
Humidity | Relative humidity (percent). |
Include LL Regain | Indicate whether to include the effects of live load in your losses. |
Time at… | Release: Time when release happens. Used in the loss calculation for transfer. Erection: Time when erection happens. Used in the loss calculation for erection and construction. |
For more information on how prestress losses are calculated, see Prestress Losses.
Load Combinations
Load combinations can be enabled and disabled by using the include check box. Auto select load combinations will turn on only the combinations which match your load input’s load types.
Strength Combinations
Import default strength and service combinations from the currently selected specification. You need at least one strength combination to run the analysis.
Service Combinations
Import default strength and service combinations from the currently selected specification. You need at least one strength combination to run the analysis.
Settings
Deflection / Camber Options and Multipliers
Input | Description |
|---|---|
Span Options | This input determines what 'L' to use when determining the allowable deflections Main Span: Sets L to the distance between supports Current Span: Sets L to the distance between the nearest left boundary condition and nearest right. For cantilevers this will use the cantilever length. Total Length: Sets L to the length of the member. |
Allowable Deflection | Sets the limit for deflection multipliers for both total and live load deflections. The deflection limit is always L, as defined above, divided by the inputted value. |
Transform Reinforcement | Tells the program how to handle reinforcement transformation when calculating section properties for deflections. For more information see Transformed Section Properties. |
Use mild to reduce deflection multipliers | Tells the program to follow the PCI Design Handbook to reduce the camber and deflection multipliers based on the ratio of As to Ap. |
Section Properties | Tells the program at what location the section properties should pull from. Varying: Tells the program to allow the section properties to vary down the length of the member. The section properties will be pulled for all locations. Midspan: Tells the program to use the midspan section properties as the section properties for all locations. At Supports: Tells the program to use the section properties at the supports. The software checks above both supports and uses the lower of the two section properties. |
Stiffness multiplier | Applies the given multiplier to the product of EI in the calculation of deflections. |
Flexure
Input | Description |
|---|---|
Method | Selects the method by which the program will compute the force in the concrete. |
Neutral Axis | Selects which neutral axis will be used for flexure capacity. Uniaxial: Will not rotate the neutral axis Biaxial: Will rotate the neutral axis so the section reaches static equilibrium |
Ignore shear when checking 1.2Mcr | Ignores the limitation on 2.0 Vu < phiVn when checking Mcr |
Ignored Distance | How far from the members end should be ignored when checking flexure capacity |
Reinforcement Strain Limit | For mild members only: Will check that the steel strain at the controlling flexure section is at least the value input in this box. If it is not, a warning will be shown. |
Shear
Composite Behavior | Tells the program to use either the precast section for shear, or the full composite height for shear. If the composite height is used for shear the minimum concrete strength is used. |
Treat as Slab | If the member is being treated as a slab, it allows Vu to go up to phiVc before reinforcement is needed. This option allows the user to apply ACI 318-14 7.6.3.1. Note that it does not check the height requirement of this provision. |
Shear Horizontal
More information on these options can be found on Horizontal Shear.
Method | Can selected either the ACI General Method or the PCI Design Handbook method. |
Shear Force Considered | For the ACI method only. |
Horizontal Shear Stress | For the ACI method only. This option controls which method should be used for determining the horizontal shear stress. VQ/Ib is typically considered an elastic response where V/bd can be used for both elastic and elastic responses. |
Use effective mu for shear friction | The effective coefficient of friction from the PCI Design Handbook will be used if checked. This is only valid, per PCI, if no load reversal is present. |
Compression Steel | Additional steel in the slab. This steel is assumed to be yielding in compression and produces additional compression stress in the top slab. |
Torsion
Method | Selected whether to use the ACI Method, Zia Hsu method (with plate bending near ends) or slender spandrel for handling torsion |
Transfer
Support Locations | Picking what boundary conditions to use for the transfer stage. |
Compression Limits | Limits for compression. |
Tension Limits | Limits for tension. If this value is exceeded, reinforcement will be required. |
End Zone | The end zone limits for transfer are within the computed transfer length of the ends of the member. |
Allowable Bar Stress | ACI Limit: Uses the minimum of 0.6 times the bar yield and 30 ksi as the allowable bar stress PCI Recommendation: Uses the minimum of the bar yield and 60 ksi as the allowable bar stress. |
In-Place Service
% Live Load Sustained | How much of the live load is sustained. This value is used for both stress computations, and loss computations for creep. |
Mod. Rupture | Modulus of Rupture |
Skin Reinforcement Cover | Skin cover to be used for serviceability cracking requirements. |
Compression Limits | Limit for compression stresses for both sustained load and total loads. |
Tension Limits | Limits for tension for when the member changes from Class U → T → C |
End Regions
Input | Description |
|---|---|
Limit shear near supports | This options limits Vu near the supports for ACI 318-14 9.4.3. By checking this options the shear demand will stop increasing when within the critical distance from the support. Note that shear is still checked within this distance, the demand just no longer increases. |
Limit torsion near supports | This options limits Tu near the supports for ACI 318-14 9.4.4. By checking this options the torsion demand will stop increasing when within the critical distance from the support. Note that torsion is still checked within this distance, the demand just no longer increases. |
Check shear / torsion within critical distance | If unchecked, shear and torsion design will not be checked for errors. The entries will also be removed from the output. |
Note: For ledged members (IT Beams, L-Beams, Spandrels) the height of the member uses the ledge height when computing the critical distance.
Development Options
Ktr | Value to fine tune development length calculations |
Bar Confinement Provided | The bar confinement input is used for computing both the development length of hooked bars in tension and headed bars in tension. This determines if development lengths should be increased through the use of the confining reinforcement factor and the parallel tie reinforcement factor respectively. |
Development multipliers | Multiplier to apply to the computed development lengths |
Stress Calculation Options
Use Principal Axis | If turned on, the program will account for member asymmetry when computing stresses. |
Ignore Horizontal Strand Eccentricity | If turned on, the lateral eccentricity for strand will be set to 0 when calculating stresses. |
Transform Reinforcement | Tells the program how to handle reinforcement transformation when computing section properties for stresses. For more information see Transformed Section Properties. |
Ignore Topping Stresses | If enabled, the program will not check topping stresses. |