Wind Pressure and Seismic Resistance Analysis of Aluminum Veneer Curtain Wall

As the building exterior envelope structure, aluminum veneer curtain wall does not bear the load of the main building structure, but needs to withstand various external forces such as wind load, seismic action, and temperature action. Its wind pressure resistance and seismic performance directly determine the structural safety and service life of the curtain wall. The relevant design, calculation and construction must strictly comply with the current national specifications such as Load Code for the Design of Building Structures (GB 50009, aligned with ASCE 7-16), Code for Seismic Design of Buildings (GB 50011, aligned with ASCE 7-16), and Building Curtain Wall (GB/T 21086). The safety and stability of the curtain wall under various extreme working conditions are ensured through scientific structural design and calculation.

Wind Pressure Resistance Performance Analysis of Aluminum Veneer Curtain Wall

Wind pressure resistance is the core mechanical performance index of aluminum veneer curtain wall, which refers to the ability of the curtain wall to resist deformation and damage under wind load. It is divided into 9 grades according to GB/T 15227 standard. The higher the grade, the stronger the wind pressure resistance.

Core Influencing Factors and Calculation Principles of Wind LoadThe wind load acting on the aluminum veneer curtain wall is mainly determined by parameters such as wind pressure height variation coefficient, wind load shape coefficient, gust factor, and basic wind pressure. The core calculation principles are as follows:

Basic wind pressure: It is taken according to the 50-year return period basic wind pressure of the area where the building is located. For super high-rise buildings, coastal typhoon-prone areas, and important public buildings, it must be taken according to the 100-year return period basic wind pressure, and shall not be less than 0.3kN/㎡;

Wind pressure height variation coefficient: The higher the building height, the greater the wind pressure. The wind pressure at the top of super high-rise buildings can reach more than 3 times that of the ground, which must be accurately calculated according to the building height and ground roughness category;

Wind load shape coefficient: It is determined according to the plane shape, facade form, and curtain wall grid of the building. Wind load concentration effect will occur at building corners, eaves, facade concave positions, etc., and the shape coefficient must be amplified;

Gust factor: As the envelope structure, the curtain wall must consider the instantaneous impact of gusts. The gust factor is usually 2.0-2.5 to ensure that the curtain wall can resist the impact of instantaneous strong wind.

Core Influencing Factors of Wind Pressure Resistance Performance

Base Material Thickness and Panel Size: The thickness of the aluminum plate base material is the basis for determining the wind pressure resistance of the panel. Under the same panel size, the thicker the base material, the stronger the deformation resistance. Under the same thickness, the larger the panel size, the greater the deflection under wind load, and the easier it is to deform. The minimum thickness of conventional outdoor curtain wall aluminum plate is not less than 2.0mm. For large-size panels, 2.5mm and 3.0mm thickness should be used. For super large-size panels, the thickness must be determined through special calculation.

Stiffener Design: Stiffeners are the core means to improve the wind pressure resistance of large-size panels. By setting aluminum alloy stiffeners of the same material as the panel on the back of the aluminum plate, the moment of inertia of the panel section can be greatly increased, and the deflection under wind load can be reduced. The spacing, specification and fixing method of the stiffeners must be determined through structural calculation. Usually, the dual fixing method of structural adhesive bonding + mechanical fixing is adopted to ensure that the stiffeners and the panel bear the force together and prevent the stiffeners from falling off. According to the specification, the maximum deflection of the aluminum plate panel under wind load shall not be greater than 1/100 of the short side span of the panel, and the absolute deflection shall not be greater than 20mm.

Keel System Design: The keel system is the main load-bearing structure of the curtain wall wind load. The material, wall thickness, span and spacing of the main keel directly determine the overall wind pressure resistance of the curtain wall. The main keel usually adopts hot-dip galvanized square steel, channel steel or aluminum alloy profiles. Its section specification and wall thickness must be determined through structural calculation. Under wind load, the maximum deflection of the keel shall not be greater than 1/180 of the span, and the absolute deflection shall not be greater than 15mm. At the same time, the support spacing of the keel must be reasonably designed to avoid excessive deflection caused by too large span.

Connection Node Design: The connection node is the core link of wind load transmission. The curtain wall panel is connected to the keel through the corner code, and the keel is connected to the main structure embedded parts/post-installed anchors through the connectors. The bearing capacity of all connection nodes must be greater than the tension and shear force generated by the wind load to ensure that the load can be effectively transmitted to the main building structure. Connectors, bolts and anchors must be made of stainless steel or hot-dip galvanized material to avoid corrosion leading to reduced bearing capacity. At the same time, anti-slip and anti-pull bearing capacity checks must be carried out to prevent node damage.

Optimization Design Points of Wind Pressure Resistance in Different Scenarios

Coastal Typhoon-Prone Areas: It is necessary to increase the basic wind pressure value, amplify the wind load shape coefficient, reduce the panel size, increase the thickness of the aluminum plate, encrypt the arrangement of stiffeners and keels, improve the safety factor of the connection nodes, and the wind pressure resistance grade of the curtain wall shall not be lower than Grade 5. For super high-rise buildings, wind tunnel tests must be carried out to accurately determine the wind load parameters and carry out special wind pressure resistance design.

Super High-Rise Buildings: It is necessary to consider the influence of downwind wind vibration and crosswind wind vibration at high altitude. The wind load value must be amplified by the wind vibration coefficient. The keel system adopts a through continuous design, and the connection nodes adopt a flexible adjustable design. At the same time, the wind load concentrated areas such as building corners and tops are strengthened to ensure that the overall wind pressure resistance of the curtain wall meets the standard.

Large-Span Special-Shaped Curtain Walls: For curved, hyperbolic, large-span special-shaped curtain walls, special stress calculation must be carried out using finite element analysis software to optimize the panel division, stiffener arrangement and keel system to ensure that the wind pressure resistance of each panel meets the specification requirements. At the same time, special bearing capacity checks must be carried out for special-shaped nodes.

Seismic Performance Analysis of Aluminum Veneer Curtain Wall

The seismic performance of aluminum veneer curtain wall refers to the ability of the curtain wall to adapt to the inter-story displacement of the main structure and avoid falling off and damage under seismic action. The core design principle is flexible connection, multi-layer defense, deformable, non-falling off, to ensure that the curtain wall is not damaged under frequent earthquakes, and does not fall off as a whole under rare earthquakes, avoiding secondary disasters.

Core Specification Requirements for Curtain Wall Seismic DesignAccording to GB 50011, the seismic design of curtain walls must implement the corresponding design standards according to the seismic fortification intensity of the area where the building is located and the seismic fortification category of the building:

Seismic design must be carried out for building curtain walls in areas with seismic fortification intensity of 6 degrees and above;

The in-plane deformation performance of the curtain wall must adapt to the inter-story displacement angle requirements of the main structure. For reinforced concrete frame structures, the inter-story displacement angle limit is 1/300, frame-shear wall structure is 1/400, shear wall structure is 1/500. The in-plane deformation performance grade of the curtain wall must be higher than the inter-story displacement angle limit of the main structure;

All components and connection nodes of the curtain wall must have sufficient deformation capacity to adapt to the displacement of the main structure under seismic action, and avoid extrusion and falling off of the curtain wall caused by the deformation of the main structure.

Core Design Points of Seismic Performance

Floating Flexible Connection Design: This is the core of curtain wall seismic design. The connection nodes between the curtain wall panel and the keel, and between the keel and the main structure all adopt a floating adjustable design instead of rigid fixation. Sufficient sliding clearance is reserved between the panel mounting corner code and the keel, allowing the panel to have horizontal and vertical displacement in the plane. The connection between the main keel and the connector adopts slotted hole bolt connection, allowing the keel to have vertical displacement to adapt to the inter-story deformation of the main structure, avoiding the displacement of the main structure being directly transmitted to the curtain wall panel under earthquake action, resulting in panel extrusion, crushing and falling off.

Special Design for Seismic Joints: At the seismic joints, expansion joints and settlement joints of the main building structure, the corresponding seismic joints must be set synchronously for the curtain wall. The joint width must be larger than that of the main structure joint to ensure that the panels on both sides of the curtain wall will not collide and squeeze when the main structure is relatively displaced under earthquake action. The panels at the seismic joints adopt a flexible connection design, matched with a deformable sealing system, to ensure that the integrity of the curtain wall is not damaged during the deformation process.

Multi-Layer Seismic Defense Design: The connection nodes of the curtain wall are fixed with double bolts to prevent panel falling off caused by single point connection failure. The dual fixing method of structural adhesive bonding + mechanical fixing is adopted between the stiffener and the panel to avoid the stiffener falling off under earthquake action. The support of the keel system adopts a continuous design, and each main keel has no less than 2 fixed supports to ensure that the keel can remain stable when a single support fails, building a multi-layer seismic defense line.

Lightweight Design: The aluminum alloy base material has light weight, only 1/5 of stone and 1/3 of glass, which can greatly reduce the seismic load of the curtain wall. This is also the core seismic advantage of aluminum veneer curtain wall compared with stone curtain wall and glass curtain wall. In the design process, through reasonable panel division and optimized structural design, the self-weight of the curtain wall is controlled on the premise of ensuring wind pressure resistance, further reducing the load under earthquake action and improving seismic performance.

Optimized Seismic Design for High Intensity Seismic ZonesFor high intensity seismic zones with seismic fortification intensity of 8 degrees and above, the curtain wall seismic design must be further strengthened:

Improve the in-plane deformation performance grade of the curtain wall to ensure that its inter-story displacement adaptability far exceeds the inter-story displacement angle limit of the main structure;

All connecting bolts and anchors are made of stainless steel to improve the safety factor. At the same time, the chemical post-installed anchors are encrypted to improve the anti-pull and anti-shear bearing capacity of the nodes;

The panel size should not be too large to avoid excessive panel inertia force under earthquake action leading to damage of the connection nodes;

Special finite element simulation analysis must be carried out on the curtain wall seismic system to check the displacement, stress and deformation of the curtain wall under earthquake action, optimize the structural design, and ensure that the seismic performance meets the standard.

Performance Testing and Verification

The wind pressure resistance, in-plane deformation performance (core seismic index), water tightness and air tightness of aluminum veneer curtain wall are collectively referred to as the "four performances" of the curtain wall. Before the project construction, a third-party testing institution with qualification must be entrusted to carry out laboratory type testing and issue a test report to ensure that all performance indicators meet the design and specification requirements. For super high-rise buildings, special-shaped curtain walls, and important public buildings, on-site water spray test, on-site wind pressure resistance test, and special wind tunnel test must also be carried out to fully verify the wind pressure resistance and seismic performance of the curtain wall and ensure the safety of the project.