Removals in Belfast
As the basis of the technique demands the precise survey from the relative position of two segments inside the casting cell, this becomes less accurate since the segments become shorter. The minimumpractical period of match cast segments is approximately 2.5 m, aside from one-off pier segments. The most length of segments is generally controlled by the price of lifting and moving them, which is dependent upon the dimensions from the site.
Removals Belfast
Since many box section bridges of medium span provide an average thickness with the order of 0.5 m, a 12 m wide by 3.5 m long segment would weigh some 53 tons. However, the segments at midspan could be lighter than others near the piers, where webs are often thickened.Thus the load of typical span segments will change between 45 and 70 tons. Ingeneral, a weight of segment that will not exceed 60-70 tons allows the use of easily available cranesand low-loaders.
Once the deck is wide, segments will inevitably be heavier. For instance, the segments for any 20m wide single box will weigh typically between 25 and 35 tons per metre. Thus a 3.5 m longsegment will weigh from the order of 90-120 tons.Clearly, longer span bridges use a greateraverage thickness of concrete (8.4), and consequently the segments is going to be heavier.Inmost box section bridge decks there is a pier diaphragm. In order to limit the weight ofthe pier segment to that of standard segments, extremely common practice to lessen its length,typically to 2-2.5 m. It's also often essential to lessen the weight of the diaphragm bythinking clearly about its various functions (9.6), and removing all redundant concrete.Generally, the pier segment can be used because the origin with the countercastrun, and it is sometimes cast beforehand inside a simple xedmould.
For long decks, the length of segment adopted may critically determine the number of casting cells that has to be mobilised; a rise in length may lessen the number of cells, at the expense of growing the load with the segments. The usage of lightweight concrete has been proven as economical if this means along the segments being increased and the quantity of casting cells being reduced without increasing the segment weight beyond some critical limit.
By advancing or withdrawing the stop-end segment so it penetrates more or less to the steelshutter of the casting cell, along segments might be adjusted slightly during casting, inorder to suit slightly varying span lengths. However, this could very well be impossible in the event the bridgedeck is sharply curved, since the sealing from the shutter to the stop-end segment would becompromised, causing grout leaks and untidy joints.
The designer also offers selecting adopting several lengths of segment, with the idea to adaptthem to varying spans, in order to limit the weight of the heavier segments to get a variable-depthdeck. However, if the segments within one casting run have different lengths, the castingprogramme will probably be disrupted to some degree, as the mould has to be adjusted.
It is goodpractice to minimise such changes, and where possible keep all of the segments of your castingrun at the same length.Generally speaking, the most span which may be built economically bythe precast segmental way is in uenced through the height and value from the mould, and by theweight of segments to be lifted. For instance, a 160 m span would require a mould some 8 mhigh, and the deepest span segments for any 12 m wide deck will probably weigh some 50 tons per metre, or 175 tons for a 3.5 m long segment. Clearly for too long viaducts, in which the moulds and lifting gear is going to be well amortised, the scale and weight of the segments is probably not an obstacle to selecting this method of construction.
In some special cases, lengthy, heavy segments might be justi ed. In Benaim's proposedalternative design for your Storabaelt Approach Viaducts, that includes a 4 km longseries of 164 m spans, match-cast segments 23.7 m wide or over to 8 m long were planned,weighing up to 600 tons. This was possible because powerful ? oating
The precasting of segments imposes a stricter discipline about the span lengths of viaducts than cast-in-situ construction. However, it's possible to accommodate a substantial variation byusing the following measures.
The size of segments could be modi ed by approximately ±25 mm by adjusting the position of the stopend segment inside the casting yard.The length of cast-in-situ stitches might be varied from 150 mm to a single m.Along the pier segment that could be cast away from casting cell, may be varied.For decks erected in cantilever, unbalanced cantilevers having an additional segment onone side might be adopted.As a last measure multiple segment length can be utilized.All thesemeasures were necessary for the Belfast Cross Harbour Bridges, the location where the tender design and the ways of construction were completed by Benaim, Figure 15.29 for your GrahamFarrans JV.
This technique of construction relies for its economy around the high productivity of your factory environment. The appearance of those times must recognise this, and supply segments whichare as repetitive as possible.In general, the webs and/or bottom slab can change inthickness across the span. Additionally, there are apt to be internal blisters for that anchorageofpermanent or temporary tendons, generally in the bottom and top corners of the box, and strong points for lifting the segments,
Figure 14.7. These characteristics need careful designand should happen at the same position insegments to simplify the core shutter. Good style of the blisters particularly, minimising theirprotrusion and fairing them well in to the concrete, pays dividends in simplicity of construction.The core shutter has to be able to be withdrawn that is at least labour.
It isnormally hydraulically powered, and must produce the clearance essential for removal eitherby retracting the side shutters towards the centre from the deck, or by rotating and folding the sideshutters, or with a mixture of those two movements. Inexperienced designers oftenchoose powerful prestressing units that want large internal anchorage blisters. If theblisters are extremely wide in comparison with the width from the box, there may 't be enough room between themto house the mechanical engineering necessary for retraction. Decks with external prestressing,in which the anchorage blisters are usually greater than for internal tendons, need particular care.
Removals Belfast
Falsework designers can accommodate virtually any geometry, but for an illconsidereddesign it will likely be in the cost of increasing time and labour being used, as the mouldwill must be partially dismantled for removal. The bridge designer should keepthese problems in your mind throughout the preliminary design, and then involve the falseworkdesigner at the earliest stage in the detailed design.
Removals Belfast
Since many box section bridges of medium span provide an average thickness with the order of 0.5 m, a 12 m wide by 3.5 m long segment would weigh some 53 tons. However, the segments at midspan could be lighter than others near the piers, where webs are often thickened.Thus the load of typical span segments will change between 45 and 70 tons. Ingeneral, a weight of segment that will not exceed 60-70 tons allows the use of easily available cranesand low-loaders.
Once the deck is wide, segments will inevitably be heavier. For instance, the segments for any 20m wide single box will weigh typically between 25 and 35 tons per metre. Thus a 3.5 m longsegment will weigh from the order of 90-120 tons.Clearly, longer span bridges use a greateraverage thickness of concrete (8.4), and consequently the segments is going to be heavier.Inmost box section bridge decks there is a pier diaphragm. In order to limit the weight ofthe pier segment to that of standard segments, extremely common practice to lessen its length,typically to 2-2.5 m. It's also often essential to lessen the weight of the diaphragm bythinking clearly about its various functions (9.6), and removing all redundant concrete.Generally, the pier segment can be used because the origin with the countercastrun, and it is sometimes cast beforehand inside a simple xedmould.
For long decks, the length of segment adopted may critically determine the number of casting cells that has to be mobilised; a rise in length may lessen the number of cells, at the expense of growing the load with the segments. The usage of lightweight concrete has been proven as economical if this means along the segments being increased and the quantity of casting cells being reduced without increasing the segment weight beyond some critical limit.
By advancing or withdrawing the stop-end segment so it penetrates more or less to the steelshutter of the casting cell, along segments might be adjusted slightly during casting, inorder to suit slightly varying span lengths. However, this could very well be impossible in the event the bridgedeck is sharply curved, since the sealing from the shutter to the stop-end segment would becompromised, causing grout leaks and untidy joints.
The designer also offers selecting adopting several lengths of segment, with the idea to adaptthem to varying spans, in order to limit the weight of the heavier segments to get a variable-depthdeck. However, if the segments within one casting run have different lengths, the castingprogramme will probably be disrupted to some degree, as the mould has to be adjusted.
It is goodpractice to minimise such changes, and where possible keep all of the segments of your castingrun at the same length.Generally speaking, the most span which may be built economically bythe precast segmental way is in uenced through the height and value from the mould, and by theweight of segments to be lifted. For instance, a 160 m span would require a mould some 8 mhigh, and the deepest span segments for any 12 m wide deck will probably weigh some 50 tons per metre, or 175 tons for a 3.5 m long segment. Clearly for too long viaducts, in which the moulds and lifting gear is going to be well amortised, the scale and weight of the segments is probably not an obstacle to selecting this method of construction.
In some special cases, lengthy, heavy segments might be justi ed. In Benaim's proposedalternative design for your Storabaelt Approach Viaducts, that includes a 4 km longseries of 164 m spans, match-cast segments 23.7 m wide or over to 8 m long were planned,weighing up to 600 tons. This was possible because powerful ? oating
The precasting of segments imposes a stricter discipline about the span lengths of viaducts than cast-in-situ construction. However, it's possible to accommodate a substantial variation byusing the following measures.
The size of segments could be modi ed by approximately ±25 mm by adjusting the position of the stopend segment inside the casting yard.The length of cast-in-situ stitches might be varied from 150 mm to a single m.Along the pier segment that could be cast away from casting cell, may be varied.For decks erected in cantilever, unbalanced cantilevers having an additional segment onone side might be adopted.As a last measure multiple segment length can be utilized.All thesemeasures were necessary for the Belfast Cross Harbour Bridges, the location where the tender design and the ways of construction were completed by Benaim, Figure 15.29 for your GrahamFarrans JV.
This technique of construction relies for its economy around the high productivity of your factory environment. The appearance of those times must recognise this, and supply segments whichare as repetitive as possible.In general, the webs and/or bottom slab can change inthickness across the span. Additionally, there are apt to be internal blisters for that anchorageofpermanent or temporary tendons, generally in the bottom and top corners of the box, and strong points for lifting the segments,
Figure 14.7. These characteristics need careful designand should happen at the same position insegments to simplify the core shutter. Good style of the blisters particularly, minimising theirprotrusion and fairing them well in to the concrete, pays dividends in simplicity of construction.The core shutter has to be able to be withdrawn that is at least labour.
It isnormally hydraulically powered, and must produce the clearance essential for removal eitherby retracting the side shutters towards the centre from the deck, or by rotating and folding the sideshutters, or with a mixture of those two movements. Inexperienced designers oftenchoose powerful prestressing units that want large internal anchorage blisters. If theblisters are extremely wide in comparison with the width from the box, there may 't be enough room between themto house the mechanical engineering necessary for retraction. Decks with external prestressing,in which the anchorage blisters are usually greater than for internal tendons, need particular care.
Removals Belfast
Falsework designers can accommodate virtually any geometry, but for an illconsidereddesign it will likely be in the cost of increasing time and labour being used, as the mouldwill must be partially dismantled for removal. The bridge designer should keepthese problems in your mind throughout the preliminary design, and then involve the falseworkdesigner at the earliest stage in the detailed design.