Technical English Week 4 Unit 4 Section 1

Technical English Week 4: Unit 4 Section 1: Reading Comprehension Shahrood University of Technology English for Civil Engineering Students 1

The Portal Method • The most common approximate method of analyzing building frames for lateral loads is the portal method. Because of its simplicity, it has probably been used more than any other approximate method for determining wind force in building frames. This method, which was presented by Albert Smith in the Journal of the Western Society of Engineers in April, 1915, is said to be satisfactory for most buildings up to 25 stories in height. English for Civil Engineering Students 2

• At least three assumptions must be made for each individual portal or for ach girder. In the portal method, the frame is theoretically divided into independent portals (Figure 4. 1) and the following three assumptions are made: – 1. The columns bend in such a manner that there is a point of inflection at mid-depth, Figure 4. 2(a). – 2. The girders bend in such a manner that there is a point of inflection at their centerlines. – 3. The horizontal shears on each level are arbitrarily distributed between the columns. English for Civil Engineering Students 3

• One commonly used distribution (and the one illustrated here) is to assume the shear divides among the columns in the ratio of one part to exterior columns and two parts to interior columns. The reason for this ratio can be seen in Figure 4. 1. Each of the interior columns is serving two bents, whereas the exterior columns are serving only one. English for Civil Engineering Students 4

• Another common distribution is to assume that the shear V taken by each column is in proportion to the floor area it supports. The shear distribution by the two procedures would be the same for a building with equal bays, but for one with unequal bays the results would differ with the floor area method, probably giving more realistic results. English for Civil Engineering Students 5

• For this frame there are 27 redundants; to obtain their values, one assumption as to the location of the point of inflection has been made for each of 21 columns and girders. Three assumptions are made on each level as to the shear split in each individual portal, or the number of shear assumptions equals one less than the number of columns on each level English for Civil Engineering Students 6

• For the frame, 9 shear assumptions are made, giving a total of 30 assumptions and only 27 redundants. More assumptions are made than necessary, but they are consistent with the solution. English for Civil Engineering Students 7