The requirements of Amendment No. 1 have been implemented.

Of the two alternative methods specified by the standard, it is the "Standard Method" that is implemented in RAM Frame.

The program first calculates the wind pressure at each story and on each parapet, if any. It then calculates the wind force at each story by applying the wind pressures to the story and the parapet.

The Wind Load dialog box provides the input necessary values for generating the Wind forces per BS 6399.

Terrain and Building Factor, Sb

• Site Category (Town or Country)
• Closest Distance to Sea
• Upwind Distance from Edge of Town
• Sh (for building height greater than 100m)

These values are used in the calculation of the Terrain and Building Factor, S_b per Clause 2.2.3.3 and Table 4. If H_e is greater than 100m, S_b is calculated per Section 3 as specified by Note 4 of Table 4.

Direction

• X Axis
• Y Axis

Effective Height, He

• Building Height, H
• Displacement Height, Hd

The user has the option of specifying H to be the Top Story Height plus the Parapet, the Top Story Height, or a specified height.

These values are used in the calculation of the Effective Height, H_e, per Clause 1.7.3.3, which is used in the calculation of the Terrain and Building Factor, S_b, per Clause 2.2.3.3 and Table 4.

Building Dimensions, B

• X
• Y

For buildings in which the size of each floor is the same, these dimensions would be those of the typical floor, but for buildings in which the floor size varies (i.e., inset Stories), it is necessary for the user to specify the dimensions to be used in the calculation of H_r, H_e and S_b. They are not used as the actual exposure width in the determination of the exposed area. H and B are used in the determination of the division of buildings by parts as specified in Clause 2.2.3.2 and Figure 11, which gives H_r for each part.

Wind Speed, Vs

• Basic Wind Speed, Vb
• Altitude Factor, Sa
• Direction Factor, Sd
• Seasonal Factor, Ss
• Probability Factor, Sp

These values are used in the calculation of the Site Wind Speed, which is given by Eq 8:

Vs = VbSaSdSsSp

Miscellaneous items

• Dynamic Augmentation Factor, Cr
• Size Effect Factor, Ca
• Frictional Drag Coefficient, Cf
• Pressure Coefficients, Cpe

The user can either specify to use the values automatically calculated by the program, or to use a value specified by the user. Note that only the external pressure is of interest, it is assumed that the internal pressures cancel out.

The wind pressures are then calculated. The overall loads on the structure are given by Equation 7 in Clause 2.1.3.6:

Note 3 says that the (ΣP_front- ΣP_rear) term may be replaced by Σq_sC_pC_aA where C_p is given in Table 5a. The values using Table 5a are not implemented at this time. The Windward and Leeward values of C_p given in Table 5 are used instead. The program first calculates pressures so that those values can be reported, then it calculates forces. So for the total pressure at any given level, Equation 7 becomes:

Pressure = 0.85qs (CpWindward - CpLeeward) Ca (1 + Cr)

where

Cr	=	Dynamic Augmentation Factor defined in Clause 1.6.1 and Figure 3, and is input by the user.
Ca	=	Size Effect Factor defined in Clause 2.1.3.4, and is input by the user.
CpWindward and CpLeeward	=	Windward and Leeward Net Pressure Coefficients given in Table 5. In that table Cp is a function of D and H. When the structure is not of uniform size at every level (such as inset Stories), DStory is used for D. Figure 12 indicates that H is Hr. So in Table 5, D and H correspond to DStory and Hr respectively. Since these values may vary from level to level, the value of Cp used may vary. Alternatively, the user may specify the value of Cpto be used at all levels.
qs	=	Dynamic Pressure defined in Clause 2.1.2. It is given by Equation 1:

qs = 0.613Ve2

where

Ve

=

Effective Wind Speed defined in Clause 2.2.3 and is given by Equation 12:

Ve = VsSb

where

Vs

=

Site Wind Speed defined in Clause 2.2.2 and is given by Equation 8:

Vs = VbSαSdSsSp

where

V_b, S_α, S_d, S_s and S_p are input by the user as explained above.

S_b = Terrain and Building Factor defined in Clause 2.2.3.3 and is given in Table 4 for H_e less than 100m. In Table 4, H_e is as defined in Clause 1.7.3.3, and is the greater of:

He = Hr - Hd

He = 0.4 Hr

where

Hd	=	Displacement Height and is input by the user.
Hr	=	Reference Height as defined in Clause 2.2.3.2 and given in Figure 11. For some building configurations (when the height is greater than the width) this value may vary with each level, hence Sb

The wind pressures at each Story and at the top of each parapet, if any, are calculated.

The friction pressures on the sides of the structure are then calculated. Friction forces on the side faces of the structure are given in Clause 2.1.3.8 by Equation 7a:

Pf = qsCf AsCα

Since the program works with pressure, this equation becomes:

Friction Pressure = qsCfCα

where

Cf	=	Frictional Drag Coefficient and is given in Table 6 of Clause 2.4.5, and is input by the user.
Cf and Ca	=	defined previously.

Per Clause 2.4.5, this pressure should be applied only when D > b, and then only to Zone C. In Clause 2.4.1.3, b is defined as the smaller of B and 2H. Figure 12 indicates that H is H_r. When the structure is not of uniform size at every level (such as inset Stories), B_Story is used for B. Likewise, D_Story is used for D. The length of Zone C is then given by D - b.

The friction pressures at each Story and at the top of each parapet, if any, are calculated.

The friction pressure is applied to both side faces along the length C and Story height and the resulting force is split between the Story and the Story below. The contribution of the frictional forces Pf is taken to act in the direction of the wind and is added to the contribution of the normal pressure forces using vectorial summation, as per the requirements of the standard.

Clause 2.1.3.7 requires that an allowance for asymmetry of loading be made. Note 1 says that those effects "may be accounted for by reducing the design wind load by 40% on those parts of the structure where the effect of the load is beneficial." Note 2 says that "torsional effects on buildings may be accounted for by displacing the loads on each face horizontally by 10% of the face width from the center of the face." It can be shown that for a regular shaped building such as what the Wind load generation feature is intended for, the wind forces given by the methodology defined by Note 2 is more onerous than those by that of Note 1. (In the Note 1 method, 100% of the design pressure would be applied to half of the structure, and 60% to the other. This means that, overall, 80% of the design pressure is applied. The 'centroid' of this arrangement of pressures is offset at 6.25% of the face width from the center of the face. In contrast, the methodology of Note 2 requires that 100% of the design pressure be applied, with an offset of 10% of the face width from the center of the face.) The RAM Structural System uses the method given in Note 2.

For each Direction (X Axis and Y Axis) specified by the user in the Wind Load dialog box, the program creates three load cases, for a total of six. It creates three X-direction cases: one with the load applied to the centroid of the pressure area, one with the load applied with 10% eccentricity (i.e., offset by 10% of the Y-dimension of the Story) in the positive Y-direction and one with the load applied with 10% eccentricity in the negative Y-direction. Likewise for the three Y-direction load cases.

RAM Frame generates the code-specified wind loads in the directions and magnitude given below. The possible load directions in a typical run consist of: