Wind Load Tests

Essentially, wind tunnel testing targets performance-based design criteria. The purpose of structural wind loading is to determine the foundation and lateral wind forces that will act on a building prior to construction. In general, the higher the wind load, the more building material is required to ensure that the structure can withstand these wind forces. Actual wind loads have been confirmed to be much lower than those determined by a code-based approach. Therefore, wind tunnel testing allows for reductions in materials and associated costs.

It has been determined that a measurable reduction in wind loads (around 40 percent on average) can be achieved through wind tunnel tests, and load reductions can sometimes be even greater.

For the general structural design of buildings, wind loads are divided into two groups:

• Vertical loads, such as the weight of the structure itself (i.e. dead loads) or the weight of the building's contents (i.e. live loads), often govern the design of slabs and columns.
• Lateral loads, such as wind loads, generally govern the design of the core and any shear walls.

Both of these can form a significant portion of the building mass.

For tall buildings, wind has a significant impact on building design. For low-rise buildings, vertical loads are often more important, although not always the case.

The European standard "EN 1991-1-4 Actions on structures - Part 1-4: General actions - Wind actions" describes the principles and rules for determining natural wind effects for the structural design of buildings and civil engineering works for each of the loaded areas considered. This includes the entire structure or parts of the structure or elements attached to the structure, such as components, cladding units and their fixings, safety and noise barriers.

This standard is applicable to:

• Buildings and civil engineering works up to 300 m high
• Bridges with a span of no more than 200 m

This standard aims to predict characteristic wind effects on land-based structures, their components and extensions.

This standard also applies to structures less than 1 km from the main coastline. For structures more than 1 km from the main coastline, the terrain effects defined in this standard do not apply.

This standard does not provide guidance on mixed wind climates, such as non-synoptic winds, e.g., storms, downdrafts, microgusts, tornadoes, and does not provide guidance on how to account for local effects, e.g., thermal effects, funneling, strong Arctic thermal surface inversion, and similar effects.

This standard deals with simplified procedures for dynamic effects, mostly based on the assumption of a dominant single-mode response. General criteria for performing a full dynamic analysis under aerodynamic excitation are outside the scope of this standard. Wind pressure effects from passing vehicles are also outside the scope of this standard. EN 1991-2 applies to wind effects from passing trains.

For the purposes of this standard, the following definitions apply in addition to the terms and definitions given in EN 1990, ISO 2394, ISO 3898 and ISO 8930.

• The actual fundamental wind speed is the characteristic 10-minute average wind speed.
• The basic wind speed is the actual basic wind speed modified to account for the annual probability of exceedance, wind direction, season, and altitude (if necessary).
• The mean wind speed is the basic wind speed modified to account for the effects of terrain roughness and altitude above sea level.
• The crest factor for turbulence is the factor corresponding to a wind duration of approximately 3 seconds, which corresponds to standardized wind durations at weather stations.
• The pressure coefficient is the coefficient that gives the pressure on the surfaces of buildings or civil engineering works. External pressure coefficients are applied to external surfaces, internal pressure coefficients are applied to internal surfaces.
• The net pressure coefficient is the coefficient that takes into account the pressure difference across a surface.
• The force coefficient is the coefficient that takes into account the overall effect or effect per unit length of wind on a structure, structural element or component, including friction if not specifically excluded.
• The coefficient of friction is the coefficient that takes into account the effects of wind friction on the external surfaces of buildings and structures.
• The background response factor is the factor that allows for the lack of full correlation of pressure on structural surfaces.

Among the numerous testing, measurement, analysis and evaluation studies carried out for businesses in various sectors, our organization also provides wind load testing services with its trained and expert staff and advanced technological equipment.