RAPT

STRUCTURAL CONCRETE DESIGN
'A Comprehensive Computer Package for the Design of reinforced and Prestressed Concrete Structures'


DETAILS

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Typical Section Graphics

 

The RAPT analysis and design package for reinforced and post-tensioned concrete structural systems has been written and developed by practising structural engineers as an everyday design tool.  It is comprehensive in its treatment of the analysis and design of structural concrete.

RAPT is developed for use with IBM compatible personal computers, and will perform design and analysis to the following National concrete design standards:

       AS 3600 - 2001

       AS 1480/AS1481

       BS 8100

       ACI 318-99/UBC

       EUROCODE 2

       SABS 0100

       CP 65 - 1999

OTHER Codes based on those listed above can be emulated using the large range of variable default settings available in RAPT.  Also extra codes may be added on request.

Cross Section Input

 

The following design utilities are incorporated in RAPT:

  • General Concrete Member Analysis and Design
  • Concrete floor system Analysis and Design
  • General flexural concrete section design
  • Concrete column design
  • Composite concrete/steel beam design
  • Tendon Profiling

The input is fully interactive using spreadsheet format.  Typical design parameters are defaulted where relevant.  The emphasis is placed on minimizing laborious data entry, and providing maximum flexibility in design options.  Program execution proceeds interactively, progressing through the design sequence, showing all steps normally taken in standard design office procedures.

Designers may alter any decision made by RAPT on their behalf.  Data output is in a form consistent with typical presentation of structural design computations.  The output is selective, may be any combination of graphics and text and may be as detailed as desired.

 

RAPT and PARTIALLY PRESTRESSED CONCRETE DESIGN

In RAPT an integrated approach to reinforced and post-tensioned design is adopted, consistent with the concept of partial prestressing. 

Fully prestressed design specifies that a minimum compressive stress exists in the concrete under all service conditions.  That is, the concrete is at no time cracked or subject to tensile stresses.

In contrast, partial prestressing requires that structural elements comply with design limit states of ultimate strength and serviceability (as with reinforced concrete).  This rational basis for design is in accordance with the philosophy adopted in modern design codes, in which reinforced concrete design and design for full prestress represent the two extremes of structural concrete design.

In this manner, prestressed concrete represents only an extension of the concept of conventionally reinforced concrete, being essentially a material hybrid, utilizing the compressive strength of concrete and the high tensile capacity of steel: Post-tensioned concrete having obviously superior serviceability characteristics in terms of deflection and crack control.  This permits a rational and consistent approach to structural concrete design and is the philosophy adopted in the RAPT package.

 

GENERAL CONCRETE MEMBERS

RAPT analyses and designs a sub-frame consisting of the member to be designed with columns above and below. Non-prismatic concrete members with multiple concrete layers and voids can be defined using a series of trapezoidal and circular concrete shapes to define basically any concrete cross-section and elevation.

 

CONCRETE FLOOR SYSTEMS

RAPT will design the following floor systems:

-             Flat Slab/Flat Plate.

-             Beam and Slab. (1 or 2 way).

-             Slab and Band systems.

-             Beam systems, transfer beams etc.

-      Columns of any shape

 

RAPT MEMBER DESIGN TECHNICAL DESIGN FEATURES

Plan & Elevation

 

These floor systems can include any of the following standard concrete element types

-                 slab of variable depth

-                 drop panels

-                 drop caps

-                 beams/bands (upturn and/or downturn)

-                 rectangular/circular columns

-                 extra concrete layers

-                 vertical steps in all horizontal surfaces

-                 horizontal steps in all vertical surfaces

-                 sloping surfaces in all surfaces

-                 solid and void rectangular or circular elements

These last 5 options allow the designer to define members with complex shapes with virtually unlimited variations in cross-section shape if necessary while maintaining a simple method to define normal members with little shape variation.

Construction for any of these floor systems may be conventional reinforced, partially or fully prestressed concrete (bonded or unbonded), pre-tensioned.

Loads Input

 

 

 

LOADING

      RAPT creates primary load cases to allow for

-               self weight loads

-               superimposed dead loads

-               live loads (envelope)

-               wind loads (envelope)

-       earthquake loads (envelope)

-       moving loads

       Extra load cases can be added by the user to handle more complicated loading arrangements. These primary load cases can include combinations of the following load types

-               uniform distributed loads

-               linear distributed loads

-               trapezoidal distributed loads (partial length of member)

-               point loads

-               point moments

moment and shear diagram / envelope (user defined)

       Alternate/Adjacent span pattern loads are automatically generated by RAPT from the live load primary case if requested.

       Combinations of these primary load cases are defined by RAPT to create envelopes of design moments and shears for design purposes. For standard primary load cases, RAPT adds the primary load cases to the appropriate combinations with multiplying factors for the design code being used. Extra load cases are added to combinations with factors defined by the designer. Designers can over-ride the combinations created by RAPT or create extra combinations if desired.

 

Prestress Tendon Profiles

 

 

Prestress Forces & Actions


 

 

PRESTRESS

       Tendon profiling may be automatic, semi-automatic or fully manual allowing several different profiles in any given run. Tendons may start and end at any user defined location along the member, thus allowing the definition of different tendons between pour strips for large floor slabs to correctly model the tendon forces.

       At a cross-section, different tendons may be at different heights and have different prestress forces.

       Tendons are not required to extend over the full length of the member. Some sections can be plain reinforced concrete while other sections are prestressed.

       Tendon Profiles can be

-                 straight

-                 parabolic (with or without straight portions)

-                 single point load

-                 double point load. 

Transition / reverse curves are automatically calculated and checked by RAPT to ensure that they are buildable.

       All prestress loss calculations are carried out automatically, followed by a complete equivalent load analysis, removing a majority of the time consuming computation associated with these aspects of prestressed concrete design. 

       Secondary (hyperstatic) prestress effects are calculated automatically and are fully incorporated in the analysis and design. The designer can control the use of these in the load combinations.

 

REINFORCEMENT

       The designer can specify different cover zones in different areas of the member.

       The designer can specify simple or complex reinforcing patterns in the input to be checked for capacity and their effect on ductility, shear and deflections.

       RAPT automatically allows for end development of defined reinforcement depending on the location of a design cross-section from the bar end.

Moment & Shear Diagrams

 

MEMBER ANALYSIS AND DESIGN

       Member/joint layouts and Frame properties are calculated automatically from the member shapes defined in the input. Modelling of columns may use either full column stiffness or the equivalent column approach and incorporate column shortening and various restraint effects.

       RAPT executes a stiffness analysis for all loads on the structure and combines them for transfer, service, ultimate and several deflection conditions using combinations specified in the relevant codes, or any user defined set of combinations. 

       Structural actions are automatically distributed in two-way systems. Designers can control the distribution factors if desired

       RAPT automatically determines the points at which design checks are performed and includes all critical points in the frame

-                 critical section at support

-                 changes in section

-                 ends of prestress tendons

-                 reinforcing bars

-                 plus at intermediate points

to provide the designer with the distribution of reinforcement required in the member

 

      Detailed reports are given at all design points (min 13 per span)

-                 moments and shears

-                reinforcement areas

-                stress conditions

-                deflections

-                shear reinforcement

-                 reinforcement spacings and bar numbers  

Ultimate Capacity Results

 

 

ULTIMATE CAPACITY

      Ultimate strength checks are performed for both primary and reversal moments at all points and include checks for 

-                 existing capacity (tendons and reinforcement) 

-                 minimum reinforcement 

-                 ductility (including determining of plastic hinge locations)

-                 extra reinforcement requirements for ultimate strength 

A detailed concrete stress-strain relation is used in a moment curvature analysis to accurately analyse any cross-section configuration

Service Capacity Results

 

SERVICE CAPACITY

      Service stress checks are performed for both primary and reversal moments at all points.

       Transfer stress checks are performed for both primary and reversal moments at all points.

       A complete cracked section analysis is performed if any section is subject to tension under working or transfer loads.  The cracked section results include the tabulation of the stresses in the concrete and steel layers. Reinforcement will be added to control cracking if necessary and requested by the designer.

      Crack Control calculations are performed automatically in different ways depending on the system type and design code.

 

Beam Shear Results

SHEAR CAPACITY

      Beam and punching shear are investigated for each span and column respectively, with complete design of shear reinforcement and spacing checks for each of the ultimate load combinations and also for the reversal case. The controlling case is reported at each design section.

       Shear enhancement calculations are performed if allowed by the design code (BS8110, CP65, SABS0100, AS3600).

 

Deflection Results

 

DEFLECTIONS

       Deflections are calculated for 4 load stages to allow for transfer, short term, permanent loading and initial loading stages using Moment Curvature principles.  The four deflections calculated are

-               transfer (self weight)

-               short term

-               long term

-               incremental

Deflection calculations allow for

-               cracking

-               tension stiffening

-               creep

-              shrinkage warping

-              time of loading

-               reinforcement layouts

-               load history.

Creep, shrinkage and tension stiffening are considered in a detailed, advanced analysis of the member which determines their effect on the curvature and deflection of the member at different loading stages. Effects of tension and compression reinforcement on deflections are allowed for in the calculation of member curvature which considers loading and creep, where appropriate, and shrinkage warping. 

For two-way systems, deflections are calculated for both column and middle strips.

RAPT represents a continuing trend towards increasingly comprehensive analysis and design software.  The traditional approach of iterative and distinct phases of analysis and design is considerably enhanced.  The design process is reduced in its duration and complexity by the interaction of the designer at various stages of design and analysis, the minimization of superfluous data entry by employing default parameters, and the ability to selectively automate those components of the design process that are repetitive and time consuming.

These elements of design are integrated in the one package, eliminating discontinuities and incompatibilities existing between both analysis and design software, and reinforced and prestressed design.

Future editions of RAPT will further develop these aspects with design detailing output in plan and section form.

Column Interaction Diagram

 

COLUMN DESIGN

RAPTís column design utility offers designers complete flexibility in defining complex column (bending and compression member) shapes and reinforcement patterns.

Special features include

-                 Simple column generator for circular and rectangular columns and reinforcement patterns

-                 Complex column shapes built from a range of solid and void rectangular, trapezoidal and circular quadrant shapes

-                 Complex reinforcement patterns to suit any column, bundled bars

-                 Prestressing steel patterns (pre-tensioned or post-tensioned)

-                 Generate Single interaction curve with critical points defined

-                 Generate multiple interaction diagrams for range of bar sizes

-                 Tension zones included

-                 Compare design points graphically

-                 Slenderness checks included
 

POST-TENSIONING

THE ADVANTAGES

The advantages of post-tensioned concrete floor systems are well documented, and may be summarized:

  • Slender structural systems are possible for a given support grid, thus permitting reduced section sizes and floor to floor dimensions, with consequent economies.
  • Building mass is reduced, thus savings in vertical load carrying elements and foundations are possible.
  • Serviceability behaviour is greatly improved, both deflection, and crack control giving greater resistance to corrosion.
  • Larger spans are possible giving greater flexibility in structural configuration.
  • Constructibility is, in general, improved, with reduced reinforcement congestion and fixing time.
  • High fatigue strength, and generally, ductility in overload behaviour.
  • Reduction in construction time due to earlier stripping of formwork.
  • Increased punching shear capacity.
  • Water leakage in roof slabs is greatly reduced.

In many instances partial prestressing represents the most economical and best performing structural solution.*

* RAPT allows optimisation of a prestressed concrete solution with the ability to investigate a number of possible configurations to a high degree of accuracy very rapidly.

Copyright 2013 PCDC