Risa Project Analysis: Success and Future.

The following sample essay on “Risa Project”: analyzing of Risa project, It’s success and future perspectives.

This particular project is mainly going to address the design of a frame made of steel sections using both RISA and analytic methods. The frame as shown in the figure below is composed of steel beam sections and columns which are pinned to the foundation.

Normally, when supports are pinned, this is normally very economical for foundations since there is no moment transfer from the column to the foundation compared to when the supports are fixed to the foundation.

Figure 1. 2-D frame to be analyzed and designed.

The frame is loaded as shown in figure 1 above and w denotes a distributed dead load of 500 lb/ft and a distributed live load of 1000 lb/ft. As the specifications, the design will be restricted to the use of A572 grade 50 steel and this has to lead to the selection of the lightest and most economical W sections.

The beams tying the columns are spanned art an equal distance of 20 feet each while the columns are 15 feet long. Also, a value of 1 for k will be assumed for the design of columns. The use of grade 50 steel generally means that the yield stress should not exceed 50 k/si.

LOADINGA’s mentioned earlier, the beam was subjected to a uniformly distributed dead and live load of 500 lb/ft and 1000 lb/ft respectively. This is shown in the figures below

Figure 2. Dead load on the beam

Figure 3. Live load on the beam

After this, the load combinations were then developed in accordance to ASCE 7 whereby two load cases were adopted as shown below

LC 1-1.4DL=1.4?500=700 lb/ft

Figure 4. Load Case 1

LC 2-1.2DL+1.6LL=1.2?500+(1.6?1000)=2200 lb/ft

Figure 5. Load Case 2

ANALYSIS

Shear, Bending Moment and Axial Force DiagramsShear force diagrams are usually very important during structural analysis because they show the distribution of shear forces within the member in question. Normally, horizontal members experience the greatest shear forces at the supports and therefore it should be ensured that adequate section sizes are provided so as withstand the said forces.

Figure 6. Shear Force Diagram

Figure 6 is a clear indication that the highest shear forces are experienced at the supports.

Bending moment diagrams on the other hand always show the distribution of moments along members both horizontal and vertical. The maximum sagging moments are mostly experienced at mid span of horizontal members while the maximum hogging moments are normally experienced at column supports. Steel sections should therefore be provided with the capacity to sufficiently resist the ultimate bending moments

Figure 7. Bending Moment Diagram

It is also important to note that since the columns are pinned, the moments at the base are zero and as a result maximum moment is experienced at beam column intersections.

Axial force diagrams are mostly used for column analysis and design. This is because they show the axial forces that columns are subjected to upon loading. This is shown in the figure below

Figure 8. Axial Force Diagram

Member stressesUpon loading, structural elements are normally subjected to member stresses the magnitude of which depends on the applied loads. The member stresses for this particular frame are as shown below

Figure 9. Member Stresses

DESIGN

For this particular project, the design was conducted using both analytical methods and RISA after which a comparison of the two was done.

ANALYTICAL METHODS

Beam Design

For purposes of this design, an initial section of W10X15 was assumed and from the bending moment diagram, the maximum moment, 59.4 k-ft was used.

mu=59.4 k-ftFrom table 1-1 of the manual, 15th edition,

bt2tf=7.410.38?EFy=0.38?2900050=9.15>7.41Therefore the flange is compact.

The web is always compact for all shapes in the manual for Fy less than or equal to 65 ksi.

Mn=Mp=FyZxTherefore,

Zx=mu?bFy59.4?120.9?50=15.85 in3This section is adequate since from the manual, Zx is given by 16 in3Shear check

From the shear force diagram,

Vu=23.02 kFrom the tables,

?Vn=69 k>Vu(23.02)Therefore the section is adequate for shear

Deflection check

The section is inadequate in deflection but RISA will be used to suggest a better section

Column Design: For purposes of this design, an initial section of W10X17 was assumed and from the axial force diagram, a maximum compressive load of 24.032 kips was used.

Column slenderness is therefore calculated as shown below: Since the column slenderness is found to be greater than 1.5, the strength fue to compressive stresses can therefore be calculated as shown below

KASSESMENTRISA was used to carry out the design and the initial sections that were used for this particular design are as follows,

For the beam, a random section of W10X15 was used while for the column design, a random section of W10X17 was used. Despite this, RISA however suggested other suitable sections which leaves the designer with the liberty to choose any desired sections. It was however confirmed the initial sections which were randomly selected for the design were not as adequate since the one for beams was failing in deflection while the one for columns was not sufficient to bear the compressive stresses. Both the sections were however compact. The primary design data for the members is as shown below

Figure 10. Primary design data

The suggested section sizes by RISA were then compiled on excel and are as shown in the figure below

Figure 11. Suggested Section Sizes

It could therefore be seen that W10X19 could comfortably work for both the columns and the beams.

CONCLUSION

It can be concluded that the project was generally a success mainly because the design worked as was expected and the selected sections were conservative and very economical. During the project, it was discovered that the results obtained from analytical methods are not any different from whatever is obtained from RISA. This is mainly because RISA uses the very same formula and sections which are found in the Steel Construction Manual to perform computations. Therefore, a basic understanding of the principles of analysis and design would really help a designer when using RISA so as to come up with the most economical sections. During this project, it was also noted that when keying in values into RISA and also when inputting the load combinations, the designer should be very keen so as to avoid making mistakes. This is because such mistakes could lead to erroneous results thereby leading to failure upon construction.