What's New in CONNECT Edition V9.6

This document describes new or enhanced features of STAAD Foundation Advanced (SFA) since the CONNECT Edition V9.5 (Release 9.5.0.62). 

Major Enhancements

1. The 2019 edition of the Canadian concrete code A23.3 is now available for isolated footings in SFA’s General & Toolkit modes.

Salient features

The footing(s) can be designed to service and ultimate load cases/combinations which are created within the SFA environment, as well as to those imported from a STAAD.Pro superstructure model.

From the standpoint of the size of the footing, two types of design are available.

1. Set Dimension where the user specifies the dimensions and the program determines if that size is sufficient to carry the loads.
2. Calculate Dimension is the other design method where the program starts from a user specified minimum size and increments it iteratively till a satisfactory size is obtained.
3. The column can be located eccentrically with respect to the center of the footing. The soil pressure calculation will account for the moments caused by the eccentricity.
4. The lateral loads from the column reactions (FX and FZ) are assumed to act at the top of the footing in the absence of a pedestal, and at the top of the pedestal if a pedestal is present. These forces are multiplied by the thickness of the footing (or footing + pedestal) and added to the moments from the column reactions for calculating the soil pressures.

Load combinations can be generated to the 2005 edition of the NBCC code within the SFA environment provided that the column reaction loads for primary load cases, categorized as Dead, Live, Wind, Seismic, etc., have been specified or have been imported from the STAAD.Pro model. Alternatively, the combinations can be specified in the STAAD.Pro superstructure model and, after the analysis of that model, the support reactions for those combination cases can be imported into SFA for the service and ultimate checks.

In both modes – General and Toolkit – from the standpoint of load cases and/or combinations, the minimum that needs to be present is either A or B, where,

A: One primary load case

B: One service load case/combination, and, one ultimate load case/combination

Checks performed for service load cases/combinations

• Soil pressures are calculated for each service load combination that is included in the isolated footing job. The forces acting at the founding level are computed from the following sources:

1. forces and moments on the footing from the column in that combination case
2. selfweight of the footing
3. soil weight
4. surcharge load

Items 2, 3and 4are multiplied with the factors specified in the “Selfweight and Deadweight Factor table” corresponding to the load case being designed.

• For each service load that is solved, the maximum soil pressure is compared with an allowable bearing pressure. Under Global Settings, the engineer can choose to define the allowable soil pressure input value as being of the type “Gross” or “Net”. The resulting “Gross” allowable pressure at the founding level is calculated and further factored by the value in the “Pile/Soil Bearing Capacity Factors” table to arrive at the maximum permissible soil pressure for the load case being evaluated. The footing is considered to have “Passed” this check if the maximum soil pressure for the load case being solved is less than the permissible soil pressure.
• For column reaction loads that cause uplift, the footing size is increased (in the case of Calculate Dimension) till the weight of footing and soil after multiplication by the appropriate factors is large enough to counter the uplift force. For Set Dimension, a net upward force implies a footing that is not in contact with the soil, and the footing is deemed to have failed.
• Stability checks – For each combination case, the factor of safety against forces that cause sliding and moments that cause overturning are computed. The footing is considered to have Passed this check if the computed factor of safety exceeds the user-specified minimum required factor of safety.
• The area of the footing in contact with the soil is calculated for each combination case. The contact area for cases where P (the force) and MX and MZ (the moments) are such as to cause partial uplift is calculated using an iterative method. The check is deemed to have Passed if the computed contact area exceeds the user-specified minimum required value.
• If the water table level is above the founding level, buoyancy effect is considered as contributing to the de-stabilizing effects. It is also considered for calculating the maximum soil pressures under partial uplift conditions.
• For each of the aforementioned checks, if the safety criteria described above is not met (meaning, the footing does not pass that check), the footing is considered to have Failed for the Set Dimension type of design, and, leads to another iteration (increase in dimensions followed by another round of the above calculations) for the Calculate Dimension type of design.

Checks performed for ultimate load cases/combinations

After the service level checks described above are computed and the footing is found to be safe for all those checks, the soil pressures are calculated for the ultimate load cases/combinations. Following this, the program calculates the bending moments, oneway and twoway shear forces which are then used in the following checks.

• Design for flexure along both principal directions. Facilities are available in the program’s UI for specifying the “specified compressive strength of concrete”, “specified yield strength of steel”, minimum and maximum permissible bar sizes, etc. The reinforcement bar library for Canada is built into the program and used for flexure design.
• Check for oneway shear along the 2 global vertical planes. This check is performed based on the assumption that the entire shear has to be resisted by concrete alone, meaning, no shear reinforcement is provided.
• Design for twoway (punching) shear. The column is treated as Interior, Edge or Corner on the basis of some empirical rules. As in the case of oneway shear, for this calculation too, design is performed based on the assumption that the entire shear has to be resisted by concrete alone, meaning, no shear reinforcement is provided.
• Development length checks. If the required development length exceeds the available, this condition is not treated as a failure. Instead, a warning is displayed for Set Dimension, as well as for Calculate Dimension if no more iterations are possible. The reason is that the necessary length can be mobilized through a combination of bends and/or hooks.
• Check for bearing from column reaction.
• The punching and bearing checks are performed for only those load cases where the column exerts a downward force on the footing. Meaning, column reaction loads that cause uplift are ignored for these checks.

The above-mentioned checks are generally similar to the ones performed for other codes such as ACI 318. The following table shows the list of the equations and sections of the Canadian code that are used in the concrete design checks for the ultimate load cases.

Description	Section of the A23.3-2019 code
Minimum thickness of the footing	13.2.1, 13.2.3, 15.7
Effective depth for oneway shear	3.2 (Symbols)
Effective depth for twoway shear	13.3.1.2
Neutral Axis factor β1	Equation 10.2, section 10.1.7 (c)
Concrete Strength Factor α1	Equation 10.1, section 10.1.7 (c)
Concrete Density Factor λ	8.6.5.a (Normal density concrete assumed)
Maximum Concrete Strain	10.1.3
Concrete Stress Distribution	10.1.7
Neutral Axis Depth & Ductility clause	10.5.2
Resistance Factor for concrete φc	8.4.2
Resistance Factor for reinforcement φs	8.4.3
Compressive & Tensile strengths of concrete	8.4.2
Maximum yield strength of reinforcement	8.5.1
Stress-strain curve for concrete & steel	8.5.3.2
Modulus of elasticity of steel	8.5.4
Lower & Upper limits for concrete strength	8.6.1.1
Minimum reinforcement for flexure	Smaller of (7.8.1, 10.5.1.1)
Cracking Moment & Modulus of rupture	8.6.4
Factored Shear Resistance of Concrete	Equation 11.6, section 11.3.4
Maximum Factored Shear Resistance of concrete	Equation 11.5, section 11.3.3
Effective web width for shear capacity calc	11.2.10.1
Shear capacity factor β	11.3.6.3(b), 11.3.6.3(c)
Maximum size of coarse aggregate for β calculation	20 mm (assumed), 11.3.6.3(b)
Critical location for oneway shear	11.3.2
Critical location for twoway shear	13.3.3.1
Factored punching shear stress resistance	Equations 13.5, 13.6, 13.7, section 13.3.4.1
Reduction in effective depth for punching	13.3.4.3
Unbalanced moment (UBM) effects	13.3.5.3, 13.3.5.4 and 13.3.5.5
“J” and other terms in UBM effects	Section 8.4.4.2.3 – ACI 318-2014
Concrete Bearing Check	10.8.1
Development Length calculation	12.2.3, 12.11.3

Output from the program

The following results are available for viewing through the program’s calculation reports.

1. Maximum soil pressure at each corner of the footing and the associated load case.
2. Load case found to be responsible for the final footing plan size if the design type is Calculate Dimension, and the corresponding Contact Area percentage.
3. Details of the sliding and overturning checks for each service load case, along with highlighting of the smallest factor of safety for the two criteria.
4. Soil pressures and contact area for each ultimate load case.
5. Details of flexure design for the longitudinal and transverse directions. Maximum moment for which design is performed and the associated load case, moment capacity, bar size and spacing, and other related information.
6. Details of check for oneway shear for the two principal planes. Maximum shear force for which design is performed, shear capacity of concrete, and other related information.
7. Details of check for twoway shear. Maximum shear force for which design is performed, shear capacity of concrete, and other related information.
8. Details of the check for column bearing on the footing.
9. Development check details – required and available development lengths, and associated values.

2. The 2019 edition of the Canadian concrete code A23.3 is now available for mat foundations in SFA’s General mode.

Salient features

Mats too are designed to service and ultimate load cases/combinations which are created within the SFA environment, as well as to those imported from a STAAD.Pro superstructure model. The workflow is as follows.

Either 

• Imports a superstructure model from STAAD.Pro. This brings in the support reactions and column/pedestal data from that model into SFA

or

• Start with a blank model in SFA, define the locations of column supports (if any) and assign the column sizes and loads acting on the foundation through those columns.
• Create a mat foundation job and choose the code as Canadian (A23.3-2019). Select the load combinations (categorized into Service and Ultimate) for which the mat should be analyzed and designed.
• Specify any additional loads on the mat if any - point loads, area loads, etc. Generate load combinations if needed. (Load combinations from the SS model can also be imported through Step (1)
• Define the mat boundary and mesh it to produce a finite element model of the mat. Specify the mat thickness to be used for analysis as well as for design.
• Specifies soil supports and/or pile spring supports.
• Performs the FE analysis of the mat.
• Create a moment envelope which is a set of discrete points where the concrete design of the mat will be performed.
• Perform the flexure and punching shear checks. The program will recommend a bar arrangement for flexure for the longitudinal and transverse directions for the top and bottom surfaces. In the event of insufficient thickness as a singly-reinforced section, a failure will be shown.
• Perform moment capacity checks for a desired bar diameter and spacing.

Notes:

Design for flexure:

• Moments used in the design are based on the results of the FE analysis of the mat.
• After retrieving the moments per unit width at the various points defined by the envelope, the program transforms them to the longitudinal and transverse directions of the mat, includes the Wood-Armer effects if the user chooses to include them, and the resulting values form the basis of the design.
• At each location, for each direction and surface, the maximum value from amongst all the selected load cases is used in the reinforcement calculation.
• The procedure used in the design of each envelope point is similar to that for an isolated footing, with the “width” of the section set to one metre.
• Details of the design are reported in tables in the “Slab designer” page of the program, for a one metre width.

Design for oneway shear

• SFA does not design mats for oneway shear

Design for twoway (punching) shear

• The procedure used in the design for twoway shear is similar to that for an isolated footing. One difference is that the upward force from the soil supports beneath the column are not subtracted from the downward force from the column. Thus, a higher force than appropriate is used in the design. This produces a more conservative result than expected. UBM effects are considered in a manner similar to that for the isolated footings.

Design for the pile punching through the mat.

• SFA does not check the punching action of piles through the mat for foundations that are supported on piles.

 Output from the program consists of

a) Summary of minimum/maximum nodal displacements from the FE model

b) Summary of minimum/maximum plate element stresses and moments from the FE model

c) Summary of maximum soil pressures from the various service load cases/combinations.

d) Contact Area report for each service load case/combination. A loss of contact will be evident through a value that is less than 100%

e) Report of Sliding and overturning check for each service load case/combination.

f) Static equilibrium mismatch report in the event of instabilities that cause overturning or sliding.

g) Pile reaction summary for service and ultimate load cases/combinations.

h) Details of the flexure design checks for the longitudinal and transverse directions for top and bottom surfaces.

3. Design of pedestals on mats and isolated footings designed to the Canadian code

For the aforementioned isolated footings and mats which are designed to the A23.3 2019 Canadian code, SFA can perform the design of pedestals as a short column for the axial force + biaxial bending moments for each ultimate load case/combination that is included in the job. But, this design is presently done to the ACI metric code using the ACI Metric bar database. This is expected to be modified in a future release by enabling design to the Canadian A23.3-2019 code.

4. Punching shear check for foundations for the Indian code

For isolated footings, combined footings and mats designed to the Indian code, the punching shear check has been enhanced to include the unbalanced moment effects per section 31.6.2.2 of the code. This has also been done for octagonal footings resting on soil supporting a vertical vessel.

Defects rectified

1. An error in identification of service and ultimate cases in the job, which prevented a mat foundation from being analyzed, has been rectified.
2. Redundant messages relating to failure for certain checks like minimum contact area were being displayed during iterations for an isolated footing to the ACI code. This has been corrected.
3. The shear enhancement factor was underestimated in some situations for pilecaps designed to the Indian code. This would lead to a larger thickness than necessary. This has been corrected.
4. A length-units related error in the creation of the mat region has been corrected.
5. The weight of soil on top of the pile cap was being slightly miscalculated in past versions. This has been corrected.
6. An error that causes pedestals to fail the design for ACI and other codes in version 9.5.0.62 of SFA has been corrected.
7. An error in the determination of the pilecap thickness of "corner" piles in the pilecap module for the ACI code has been corrected.
8. In the PLANT mode, tanks with a diameter greater than 150 ft could not be designed due to a built-in limit in the program on that parameter. The limit has now been increased to 300 ft.
9. Factored overturning moment and nominal axial load were reported incorrectly for pedestal design in the Plant Mode (Vertical Vessels). This has been corrected.
10. For mat foundations, in the dialog box that comes up when control regions are created, there is a check box for instructing the program that, that region should not be designed. An error in the program caused the moment envelope points falling within these regions to be designed inspite of the above setting. This has been corrected.