Obviously all exterior walls, of whatever material, are subject to, and must withstand the ravaging effects of the nature. Curtain wall systems are the most abused of building elements being subjected to wind loading, extreme events, building movements, sudden temperature changes, driven rain, atmospheric pollution and corrosion.
Sunlight is so vital part of the human being so that human could not live without it. It provides warmth, color, visual definition and life itself. But it also creates certain problems in curtain wall design. One of these problems is its deteriorating effect on organic materials such as color pigments, plastics and sealants. The actinic rays, particularly those found in the ultra-violet range of the spectrum, produce chemical changes which cause fading or more serious degradation of materials. Another problem resulting when uncontrolled sunlight passes through the curtain wall panel is the discomfort of glare and brightness and degradation of interior furnishings. Conventionally, such effects are combated by use of some type of shading device, either inside or outside of the vision glass. A newer approach, gaining in favor, is the use of glare-reducing or reflective types of glass which provide relief without restricting vision.
In most cases, temperature creates two kinds of problems in curtain wall design: the expansion and contraction of materials and the necessity to control the passage of heat through the wall. In other words, it is the effect of solar heat on the curtain wall to create one of the major concerns in aluminium curtain wall, like the thermal movement. In addition, temperature fluctuations, both diurnally and seasonally, critically affect wall details. All building materials expand and contract to some extent with temperature changes, but the amount of movement is greater in aluminium than that in most other building materials. The control of heat passage through the wall affects the heat loss in cold weather and heat gain in hot weather. Thermal insulation of opaque wall areas become an important consideration when such areas constitute a substantial part of the total wall area, but when vision glass areas predominate, the use of insulating glass, and the minimizing of through metal or ‘cold bridges’ are more effective in lowering the overall U-value of wall.
Water, in form of rain, snow, vapor or condensate, is probably the most persistent cause of potential trouble for curtain wall facade system over time. As wind-driven rain, it can enter very small openings and may move within the wall and appear on the indoor face far from its point of entrance. In the form of vapor it can penetrate microscopic pores, will condense upon cooling and, if trapped within wall, can cause serious damage that may long remain undetected. Leakage may be a problem in a wall built of any material. Most masonry walls, being porous, absorb a good deal of water over their entire wetted surface, and under certain conditions. Some of this water may penetrate the wall, appearing as leaks on the indoor side. But the materials used in metal curtain wall are impervious to water, and potential leakage is limited to joints and openings. Though this greatly limits the area of vulnerability, it greatly increases the importance of properly designing the joints and seals.
Wind acting upon the wall produces the forces which largely dictate its structural design. On the taller structures in particular, the structural properties of framing members and panels, as well as the thickness of glass, are determined by maximum wind loads. Winds also contribute to the movement of the wall, affecting joint seals and wall anchorage. The pressures and vacuums alternately created by high winds not only subject framing members and glass to stress reversal, but cause rain to defy gravity, flowing in all directions over the wall face. Thus wind must be recognized also as a major factor contributing to potential water leakage.
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Post time: Nov-17-2022