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ANALYSIS OF SLAB ON GRADE

USING STAAD PRO

This example illustrates the usage of commands necessary to utilize the built-in generation facility togenerate spring supports for a slab on grade. The slab is subjected to various types of loading and analysis

of the structure is performed.

The numbers shown in the diagram below are the element numbers.

STAAD SPACE SLAB ON GRADE

Every STAAD input file has to begin with the word STAAD. The word SPACE signifies that the structure

is a space frame and the geometry is defined through X, Y and Z axes. The remainder of the words form a

title to identify this project.

UNIT FEET KIP

The units for the data that follows are specified above.

JOINT COORDINATES

1 0.0 0.0 40.0

2 0.0 0.0 36.0

3 0.0 0.0 28.167

4 0.0 0.0 20.333

5 0.0 0.0 12.5

6 0.0 0.0 6.5

7 0.0 0.0 0.0

REPEAT ALL 3 8.5 0.0 0.0

REPEAT 3 8.0 0.0 0.0

REPEAT 5 6.0 0.0 0.0

REPEAT 3 8.0 0.0 0.0

REPEAT 3 8.5 0.0 0.0

For joints 1 through 7, the joint number followed by the X, Y and Z coordinates are specified above. The

coordinates of these joints is used as a basis for generating 21 more joints by incrementing the X coordinate

of each of these 7 joints by 8.5 feet, 3 times. REPEAT commands are used to generate the remaining joints

of the structure. The results of the generation may be visually verified using the STAAD graphical viewing

facilities.

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ELEMENT INCIDENCES

1 1 8 9 2 TO 6

REPEAT 16 6 7

The incidences of element number 1 is defined and that data is used as a basis for generating the 2nd

through the 6th element. The incidence pattern of the first 6 elements is then used to generate the

incidences of 96 (= 16 x 6) more elements using the REPEAT command.

UNIT INCH

ELEMENT PROPERTIES

1 TO 102 TH 5.5

The thickness of elements 1 to 102 is specified as 5.5 inches following the command ELEMENT

PROPERTIES.

UNIT FEET

CONSTANTS

E 420000. ALL

POISSON 0.12 ALL

The modulus of elasticity (E) and Poissons Ratio are specified following the command CONSTANTS.

SUPPORTS

1 TO 126 ELASTIC MAT DIRECTION Y SUB 10.0

The above command is used to instruct STAAD to generate supports with springs which are effective in the

global Y direction. These springs are located at nodes 1 to 126. The subgrade modulus of the soil is

specified as 10 kip/cu.ft. The program will determine the area under the influence of each joint andmultiply the influence area by the subgrade modulus to arrive at the spring stiffness for the FY degree of

freedom at the joint. Additional information on this feature may be found in the STAAD Technical

Reference Manual.

PRINT SUPP INFO

This command will enable us to obtain the details of the support springs which were generated using the

earlier commands.

LOAD 1 WEIGHT OF MAT & EARTH

ELEMENT LOAD

1 TO 102 PR GY -1.55

The above data describe a static load case. A pressure load of 1.55 kip/sq.ft acting in the negative global Y

direction is applied on all the 102 elements.

LOAD 2 COLUMN LOAD-DL+LL

JOINT LOADS

1 2 FY -217.

8 9 FY -109.

5 FY -308.7

6 FY -617.4

22 23 FY -410.

29 30 FY -205.

26 FY -542.7

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27 FY -1085.4

43 44 50 51 71 72 78 79 FY -307.5

47 54 82 FY -264.2

48 55 76 83 FY -528.3

92 93 FY -205.0

99 100 FY -410.0

103 FY -487.0

104 FY -974.0

113 114 FY -109.0

120 121 FY -217.0

124 FY -273.3

125 FY -546.6

Load case 2 consists of several joint loads acting in the negative global Y direction.

LOADING COMBINATION 101 TOTAL LOAD

1 1. 2 1.

A load combination case, identified with load case number 101, is specified above. It instructs STAAD to

factor loads 1 and 2 by a value of 1.0 and then algebraically add the results.

PERFORM ANALYSIS

The analysis is initiated using the above command.

LOAD LIST 101

PRINT JOINT DISPLACEMENTS LIST 33 56

PRINT ELEMENT STRESSES LIST 34 67

Joint displacements for joints 33 and 56, and element stresses for elements 34 and 67, for load case 101, is

obtained with the help of the above commands.

FINISH