Week 5 Challenge

Week 5 Challenge – Explanation

Input Data:

*The height of the bridge above ground level is 9m.

*It is located in open terrain with well-scattered obstructions at a height of less than 10m.

*The pier size is 1.5m x 1.5m.

Problem:

*Calculate the design wind loads for the bridges to be designed in Mumbai.

*Apply the wind load in Staad.pro

Solution:

*Wind Load Calculation

Wind load calculation as per IS875-part3-2015

Site location – Mumbai

Wind speed (as per IS875-part3-2015-Annex-A) – 44 m/s

Design Wind Speed – Vz = Vb x k1 x k2 x k3 x k4

Where

Vz – design wind speed at height ‘z’, in m/s

Vb – wind speed, in m/s

k1 – probability factor (risk coefficient)

k2 – terrain roughness and height factor

k3 – topography factor

k4 – importance factor for the cyclonic region

From IS875-part3-2015,

k1 – 1, considering (All general buildings and structures, design life 50 years), from Table-1

k2 – 1, considering (category-2, for 10m height), from Table-2

k3 – 1, from Cl. 6.3.3

k4 – 1, considering (All other structures), from Cl. 6.3.4

Hence,

Vz = 44 x 1 x 1 x 1 x 1

Vz = 44 m/s.

Further,

Wind Pressure, Pz

Pz = 0.6 x Vz^2

= 0.6 x 44^2

Pz = 1161.6 N/m^2

= 1.16 kN/m^2

Further,

Design Wind Pressure, Pd

Pd = Kd x Ka x Kc x Pz

Where,

Kd – wind directionality factor

Ka – area averaging factor

Kc – combination factor

From IS875-part3-2015,

Kd – 0.9, from Cl. 7.2.1

Ka – 1, considering (tributary area </= 1.0), from Table-4 of Cl. 7.2.2

Kc – 1, from Cl. 7.3.3.13

Hence,

Pd = 0.9 x 1 x 1 x 1.16

= 1.044 kN/m^2.

Also the value of Pd, however, shall not be taken as less than 0.70 Pz.

Pd = 1.044 kN/m^2

0.70 x Pz = 0.70 x 1.16 = 0.812 kN/m^2

Hence ok.

Therefore Design Wind Pressure is to be taken as Pd = 1.044 kN/m^2 for up to 10m height.

Staad model – Geometry & Load application:

Geometry

Wind Load definition-apply in Staad

Load Case(1)-Wind Load (+X) Dir (Open Structure)

Load Case(2)-Wind Load (-X) Dir (Open Structure)

Load Case(3)-Wind Load (+Z) Dir (Open Structure)

Load Case(4)-Wind Load (-Z) Dir (Open Structure)

Displacement Result-Load Case (1)

Maximum BM Result-Load Case (1)

Result Summary:

A Bridge of 10m in length (with a 5m width of 3 bays) & 9m in height is modeled in staad pro.

Wind loads were calculated as per IS875-part3-2015 and applied in Staad.

Post-processing results such as displacement, and maximum BM verified.