A trussed roof is a structural framework of timbers designed to support the roof of a building. It consists of triangular units called trusses, which are made up of beams and posts connected at their ends to form a stable and load-bearing structure. Trussed roofs are commonly used in residential and industrial construction due to their strength, efficiency, and ability to span wide distances without the need for internal support columns.
In this article i shall briefly discussed about the trussed roof that is essentially a triangulated system of straight interconnected structural elements for covering a design of roof and widely used in industrial buildings, farm construction and effluent architectural design and bridge which is significantly used in world with good feeling and classical look.
Providing trussed roof is a classical appearance in civil engineering to covering roof and support to roofs, the floors and the internal loading such as service and suspended ceiling are readily provided due to support long span , lightweight, controlled deflection.
Trussed roofs is the type of pitched roof which is consist the framed structure when the span of structure exceeds the 4.80 metres and there are no inside supporting walls or partitions for the purlins.
In the designed of trussed roofs, the roof adopted the three members effectively rafters to supporting the roofing materials, purlins to used for intermediate support and trusses to used for support to the ends of purlins.
The trussed roof provide the space according to the load on the roof, position of cross walls, materials of the truss and span , generally the spacing is provide for upto 3 metres in wooden trusses, it is effectively carry the ridge section and purlin on which the common rafters rest.
Truss roof definition:- trussed roof is define as structural permanent framework generally made of timber or steel is specially designed to bridge the space above room to provide maximum ventilation and support for a roof. Trusses usually occurs at regular intervals consist of mainly three members such as top chord, webbing/ posts and bottom chord, and it is linked by longitude timber truss such as purlins.
A trussed roof consist of angles, channels, plates and eye bars. It is permanent frame structure which determine the shape of roof and ceiling typically consisting of rafters, webbing/ posts, and struts generally used to supporting roof. Roof trusses are more popular nowadays because it is 30% cheaper than rafter, using light weight materials, they can distribute the weight of roof on to the exterior wall of the house not the interior walls there are countless truss designed to create the root framing for almost any roof style.
What is truss roof?
Regarding this, “what is truss roof?”, truss roof is design of one of the basic types of structural frames are joined together in triangular configuration with the member of group of ties and struts designed and connected to formed a structural framed a large span of beam for covering roof that is known as truss roof.
Design of trusses have almost completely replaced the traditional roof construction method and widely used due to their advantage in allowing greater significant of design and in speeding up construction, while reducing the impact of external load including weather and building site are important factors contributing to widely used of trusses in covering roof.
Today construction of truss roof progressed from the early truss plates that require hand applied nails to modern truss plate that requires no nails, as the progression of truss plate are manufactured from G300 steel with a galvanised coating and also consist the stainless steel nailplates .
Today used of trusses roof are consist following properties and importance –
1. Truss plate is very effective, this is made from high grade steel to exacting tolerance that maintain the durability sustain capacity and performance require to safe truss construction.
2. Provide the quality of engineering design based on effort and experience.
3. Cutting and fitting of trussed roof member are using automated saws and computer aided control helps ensure and joints fit safely and highly accurate.
4. Trusses design are manufactured in strict accordance with design and handled safely.
5. Manufacturing of truss roof an engineered truss for installation of industrial building have requires accurate cutting, jigging and pressing to provide excellent holding significant at a low cost per truss.
6. Trussed roof features provide the installation of truss roof design low cost per truss, penetrates high density hardwoods.
7. This is eliminated the tooth bending and wood splitting.
Advantages of trussed roof
• Trussed roof consist the low cost on construction site by using lightweight material and it is 30% cheaper than rafters.
• better and experience project cost control by using advance components.
• Trusses installation of smaller dimension lumber in place of column and beam.
• this is provide pre determined engineered truss system
• Trussed roof features provide the installation of truss roof design low cost per truss, penetrates high density hardwoods.
• Trusses design are manufactured in strict accordance with design and handled safely
• Material of job site for installation of trussed roof ,cutting,jigging and fitting are installed effluent and waste material is reduced.
• Factory manufactured and farm installation and also industrial building installation components to exact span requirements.
• Provide effective flexibility in locating plumbing, work and electrical wiring.
Truss roof type
Truss roof types are follows-
1. King post truss
2. Queen post truss
3. Mansard truss
4. Truncated truss
5. Bel fast trust
6. Steel trusses
7. Composite trusses.
King post truss
King post truss is the simplest type of roofing truss, consist of basic members two top chord, a central vertical post is called as a King post in which a support for the tie beam with associated inclined members called as the struts, that is prevent the principal rafters from bending in the middle, it is also effectively adopted for King post truss span varying from 5 to 8 metres. In the king post truss span and generally spacing limited to 3 metres centre to centre.
What is a King post truss?
Regarding this, “what is a King post truss?”, king post truss is designed with the members of lower tie beam, two inclined principal rafters, two struts and a King post which is effectively used the purlins support the closely spaced rafters, rafters support the roof covering construction and tie beam mostly prevents the wall from spreading out due to thrust.
The king post truss is used for simple roof trusses and construction of short span bridge, these are associated with two diagonal members that is meet at the apex of truss, one member is horizontal beam which is serves to tie the bottom end of of the diagonals together and other members is rafters which is connects the apex to the horizontal beam below.
In the king post truss the diagonal members are called as rafters and horizontal member is a ceiling joist.
King posts are used in construction of wire braced aircraft where a King post roof truss supports the top cables or ground wire, these are mostly used in timber framed roof construction in oldest traditional and in also used in modern construction, revival architecture and structural elements in wood and metal bridges.
King post truss is effluent and significant used in requirements to support the weight of an expensive roof, feels like as effective looks and classical appearance , this type of truss roof is functionaly in design of roof and adds beauty as well, it is used in aircraft construction and earoplane to support the top cables.
Advantages of King post truss
● king post truss is used in effluently in architectural or designe of bridge.
● significant used for short span structures.
● effectively used in construction of aircraft and aeroplane to support the top cables.
● mostly used in oldest traditional in timber framed roof construction and in modera traditional adopted in rivival architectural and structural elements.
● king post trusses can save on site costs
Disadvantages of King post truss
● king post trusses have a series of supporting member that limit the use of attic space.
● king post truss is not suitable for the long span.
● this truss does not provide storage space sufficient.
● king post truss is only used for need to support the weight of an expensive roof.
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Queen post truss
Queen post truss is the type of truss roof which is differs from a King post truss in having two vertical members that is effluently kept in position of horizontal member through the upper ends of the Queen post, these type of truss are adopted for roof of span varying from 8 m to 12 metres and also a suitable strengthened provided for truss upto a span of 18 metres by using the a convenient combination of King post and Queen post truss.
In the queen post truss, generally the tops are connected by a horizontal member ,this is called as straining beam which is introduced on tie beam to counteract the thrust from compression member and two struts are adopted to join the each queen post to the principal rafters.
The queen post truss has benefits over a King post truss that is more effective and widely used due to span wider widths and it it frequently used in residential homes, public building and bridges.
Queen post truss is more popular than a King post support is that it provides more structural stability ,provide more space inside the room and make it easier to add a room at a later date.
This truss is design roof with beauty and unique style add to design of roof straight or decorative shapes with curve, and adopt a classical appearance in architectural craftsman.
What is queen post truss?
Regarding this, “what is queen post truss?”, queen post truss is having two vertical members that is effluently kept in position of horizontal member through the upper ends of the queen post, these type of truss are adopted for roof of span varying from 8 m to 12 metres and also a suitable strengthened provided for truss upto a span of 18m.
Queen post truss is a consist mostly a tension member in truss in which can long span opening in construction of roof truss than a King post truss, this type of truss is mostly tension member rather than the compression member, this is also effluent by providing the two central supporting post in design of constructing truss roof whereas King post truss uses one central supporting post.
When considering installing a queen post truss, it is important to discuss the plans with a qualified professionals to determine what problems need to be considered before beginning the project, the queen post trusses are used for spans over 30 feet and contain two perpendiculars to brace up the tie beam spanning the walls, truss for a 32 feet span, the same form is suitable upto about 42 feet span.
Advantages of queen post truss
● suitable strengthened provided for truss upto a span of 18 metres by using the a queen post truss.
● it provides more structural stability, provide more space inside the room and make it easier to add a room at a later date.
● adopt a classical appearance in architectural craftsman
● queen post trusses are used for spans over 30 feet
● these are used to design a cost effective structure.
● Simple design.
● Well accepted and used design.
Disadvantages of queen post truss
● Queen post truss is not suitable for longer span consist of greater than 40 feet.
● Poorer performance under the uniformly distributed loaded.
● Queen post truss roof is not mostly function in areas with extreme weather conditions, this is unsuitable in areas with heavy rainfall.
Mansard truss is a type of truss which is the combination of the king post and queen post truss is known as the mansard truss that is designed with two story truss with upper portion consisting of the king post truss and the Lowe portion of Queen post truss.
Mansard truss effectively used in pitched roof with consisting of two pitches, upper pitch in King post truss which is varies from 30° to 40° and the lower pitch in queen post varies from 60° to 70°.
Mansard truss roof is defined as the truss which is consist four sided gambrel style hip roof and this is effluently characterized by two slopes on each of its sides with the lower slope ,at a steeper angle than the upper.
This is associated with steep sides and double pitch, upper slopes of this type of truss roof is rarely visible from the ground, a conventional single plane roof with steep sides may be misidentified as a mansard roof.
Mansard is a curb hip roof with slopes on all sides of the building, and the gambrel is a curb gable roof with slopes on only two sides.
Mansard roof is also known as french roof which is defined as the American variation of a mansard with the lower pitches nearly vertical and larger in proportion to the upper pitches.
Now that you have a clear idea about a mansard roof that is a hybrid between a gambrel roof and a hip roof which is consist the features a similar slope design on two opposite sides, however on the other pair of sides, the mansard roof features the same sloping style .
This is become a integral part of french architecture and is quite commonly seen in many buildings located in that part of the world.
A mansard is a hipped gambrel that means the roof slopes in all four directions of the building, not just two, so if the roof slopes in all four directions but does not bend, it’s hipped but not a mansard.if it bends, but does not have four sloping sides it’s a gambrel but not a mansard, if it has four sloping sides and all of those sides bend this is mansard roof.
Advantages of mansard roof
1. Extra attic space:- Mansard roof is provide significantly more attic space relatively gable roof or hip roof due to the almost vertical bottom slope, this type of design does not compromise the space and can easily adopted widely space for needed master bedroom.
Also this type of design is provide more natural light inside the building with the help of consist the windows along the entire length of the bottom slope and also increases the space.
2. Easier expandability:- construction of mansard roof has assigned design for easier expandability, the vertical part of the bottom slope makes it easier to build additional floors on top, allows greater flexibility by the design of bottom slope relatively more popular roofing styles such as gable roofs or hip roofs.
Mansard roof makes perfect sence in flexibility to expand your house in the future according to need .
3. Aesthetical value:- Mansard roofs have elegant design, this is classical look and feel a good appearance which is important part of french architectural during the resistance period, roofing styles is executed properly.
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Disadvantages of mansard roof
1. Weather resistance:- Mansard roof is not mostly function in areas with extreme weather conditions, this is unsuitable in areas with heavy rainfall ,in fact due to the top most part of this roof is consist the low pitch, resulting it will not cope well with heavy rainfall and gain a leakage in roof.
2. High installation costs:- Mansard roof truss design installation is not simple,it is more complexity of the design,due to reasons this is carry a high installation costs.
3. Maintanence and repair costs: construction of mansard roof truss is very complexity design,due to that the installation cost of this design is very high and a high installation costs would usually point to increased maintenance and repair cost.
Truncated truss is the type of pitch roof truss which is similar to the mansard truss except that the top is effectively finished flat with a gentle slope to one side that is effluently used when a room is necessary in the roof.
Bel fast truss
Bel fast truss is a thin section of timber , associated with its top chord curved as a form of a bow which is suitably adopted for long span of 30 metres, this type of truss is effectively carry for light roof covering, this truss is also called as latticed roof truss. The bell fast roof truss is consist form of a bow which is made with a thin section of member, this truss roof is also called bow string or latticed roof truss.
Bell fast truss is effluent widely used for construction of truss roof , especially in industrial building in current centuries due to fact that it is covering larger span upto 30metre and it’s efficiency and economy behaviour for covering large clear spans, it is very classical appearance and efficient structural form with a curved top member.
Design of belfast roof truss is consists of a two piece member which is bowed top chord and a two piece horizontal bottom chords,this design is susceptible for longer span, this lattice members are nailed and notched between the top and bottom chords .this propile is very efficient for uniformly distributed loading and the thrust line coinciding with the alignment of the top chord, resulting very small forces in the lattice members.
In this design of roof truss, eaves joints are connected with the top and bottom chords,end block is used to stop the compression force in the top chord and transfer the tension force to the bottom chords.this arrangement design of truss roof is similar to the eaves details of King or queen post truss.
Belfast truss is promote sustainable roof construction in 19 th and 20 th century, it’s effective reason to used widely this type of truss roof, it’s advantages for the purpose of roofing wide span without intermediate supports are well known, it’s efficiency of structural behaviour was widely appreciated and the truss employed throughout Ireland and great Britain on industrial building, farm buildings, airfield hangars etc for span 6 m to 36 m.
● The belfast truss is a remarkably efficient structure for wide span roof construction.
● The span to height ratio which depends on the top chord radius used for a particular span is the most important influence on the truss behaviour, it is recommended that the ratio should be about 8, resulting from a chord radius equal to the span dimensions.
● The trusses in many historic buildings have suffered from the effects of water penetrations or heavy rainfall due to failure of the felt covering and leakage from the gutter , modern and effective high performance membranes and gutter linings will help eliminate the leakage problems .
● The provision of a solid boarded or plywood gusset represents a superior and suitable connection design.
● The bow string truss with simple lattice layout has a fabrication advantage over the traditional Belfast type.
Advantages of belfast roof truss
● The belfast truss is a remarkably efficient structure for wide span roof construction.
● The provision of a solid boarded or plywood gusset represents a superior connection design.
● Belfast truss design propile is very efficient for uniformly distributed loading and the thrust line coinciding with the alignment of the top chord, resulting very small forces in the lattice members.
● Bell fast truss is covering larger span upto 30metre and it’s efficiency and economy behaviour for covering large clear spans.
● it is very classical appearance and efficient structural form with a curved top member.
● Especially used in industrial building for construction of roofing cover with sustain load
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Disadvantages of Bel fast truss
● The maintanace of joints and fittings of a truss could be expensive.
● There are too much deflection for long spans.
● Bel fast truss increased constructability due to additional members.
● These are complexity design.
Steel trusses is designed with the angles riveted or welded together through the plates for the provide facilities the roof construction, this is effluently and economically suitable for spans greater than 12 metres.
The design of steel trusses is simplified and resist the both stresses compression and tension, the mild steel is easily available in the rolled section of standard shapes and sizes, this fascilaties are effectively used in the roof construction as a form of steel truss.
Steel strusses are commonly used these days for construction in pitched roofs, due to fact that this is economical, easy to fabricate, more rigid, fire proof and permanent and also effluently suitable for construction.
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Composite trusses are the type of pitch roof truss which are composed of steel or wrought iron and wooden members that is light in weight and economical, in this type of truss the steel is used for resist the tensile stresses.
In the composite trusses, the especially fitting are necessary at the junction of steel and timber.