Flexural Design of Reinforced Concrete Beams

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Page created by Meghan Myers



Welcome to the help page for Java Module A. This program allows users to investigate the flexural design of rectangular reinforced concrete beams with various end and span loading conditions. The beams are designed as singly-reinforced (i.e., compression reinforcement is ignored in the design) prismatic members with straight reinforcing bars. The design is conducted in accordance with ACI-318 Building Code Requirements for Structural Concrete and Commentary published by the American Concrete Institute [1]. Some background on the model is provided in the Overview of Module's Design Process section.


How to Use this Module

The module can be broken up into several different input sections (illustrated in Fig. 1) which the user must complete: The user can obtain help on how to complete these sections by clicking on the question mark buttons throughout the module.
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FIG. 1. Java Module A interface. Users will complete the input sections above and then click on the solve button to view the beam design in Windows 1-4.


Overview of Module's Design Process

Module A was designed based on ACI318-99. The design process is consistent with procedures covered in a reinforced concrete design course (e.g. Nilson [2]). In the Sample Laboratory Session one will find the detailed calculations and procedure for an example design. In this section, a brief overview of this process will be given.

  • Calculation of factored design moments,Mu:
  • The beam is treated as a simply supported beam with end moments in order to solve for the moment as a function of position along the length of the beam. Moment diagrams for both the max span moment loading condition and the max support moment loading condition are determined this way. These two moment diagrams form the demand curves displayed in Control Window 3 (see Fig. 1).

    The maximum moments at the critical sections can be determined from the two demand curves. These moments are used to design the beam.

  • Steel Bar Combinations:
  • Module A determines the valid bar combinations for the required steel area at each critical section using the minimum and maximum bar size numbers specified by the user in the Design Data section of the module.

    The module considers combinations of one bar size and two bar sizes. It finds the combinations with the smallest steel area and determines the maximum number of bars that can fit in the first layer given the clear spacing, sb, defined by the user in the Design Data section of the module. The module then checks these combinations for symmetry to ensure that they are acceptable configurations (see Fig. 4 in the Design 1 Calculations for acceptable bar configurations).

    Thus, the steel bar combination chosen for each critical section is the one with the smallest steel area and with acceptable symmetry and clear spacing.

  • Bar Cut-off Locations:
  • Once the reinforcing bar combinations for the critical sections have been determined, the module designs the cut-off locations for the bars along the beam length. The user specifies the maximum cut-off ratio for the span reinforcement and for the support reinforcement in the Design Data section of the module. Sample bar cut-off calculations can be seen in Design 1 Calculations..


    Sample Laboratory Session

    A sample laboratory session to demonstrate Java Module A can be found here. Calculations for one of the specimens from this session (Design 1) can be found by clicking on the link below. This PDF also contains examples of the different parameters that can be displayed in the control windows of Module A.


    Support for the development of the Virtual Laboratories for Reinforced Concrete Education is provided by the National Science Foundation (NSF) under Grant No. CMS98-74872 as a part of the CAREER Program and by the Portland Cement Association (PCA). The support of Dr. Shih C. Liu and Dr. Peter Chang, NSF Program Directors, and Dr. David Fanella, PCA Manager on Buildings and Special Structures is gratefully acknowledged. The authors also thank Prof. B. F. Spencer of the University of Illinois for his comments and suggestions. The opinions, findings, and conclusions expressed herein are those of the authors and do not necessarily reflect the views of the NSF, PCA, and the individuals acknowledged above. More information on the virtual laboratories can be found here.

    Disclaimer: No responsibility is assumed by the authors, the University of Notre Dame, or the Portland Cement Association for any errors or misrepresentations in the laboratory modules, or that occur from the use of these modules.



      ACI-318, Building code requirements for structural concrete (318-99) and commentary (318R-99), American Concrete Institute, Farmington Hills, MI, 1999, 391 pp.

      Nilson, A. Design of concrete structures, Mc-Graw Hill, Twelfth edition, (1997), 779 pp.