Hollow Structural Sections HSS columns are prevalent in many types of construction, especially in common cases such as low-rise retail buildings.

Compression Splices

In reality, HSS columns can be a great option for taller buildings as well with its aesthetically pleasing shape, simple framing connections and small footprint. As with their wide flange counterpart, transportation limits to a construction site will require these taller columns to be shipped in multiple pieces and assembled together in the field.

That is when splices become a requirement to consider as part of the design process. This article will discuss many of the splice design and fabrication requirements for various situations.

Due to typical transportation limitations on U. Another reason for a splice may be to simplify construction in the field.

Depending on the geometry and floor plan of the building, there may be times when construction sequencing requires a splice to prevent interference during installation of various portions of the building structure and components. The function of the splice is to transfer the axial, shear and flexural forces from one column piece to the next ensuring continuity of the column and stability during erection.

The splice design and detailing should consider the fabrication process and field erection as much as possible. It is critical for the splice to ensure axial forces are transmitted concentrically from the upper column to the lower column to avoid adding flexural moments due to eccentricity that have not been designed for.

To help supplement this information, several HSS splice options are discussed below.

where should splices in column be provided

When a structure is located in geographic areas with a seismic design category of B or higher, additional seismic detailing for splices may be required per AISC AISC, b. The first item to consider is the lateral force resisting system of the building and the corresponding response modification coefficient R.

Calculation of Lap length in Reinforced Concrete Structures

When R is equal to 3 or less in seismic design category B or C, seismic detailing is not required. If the value of R is greater than 3 or the seismic design category is C or higher, then the seismic detailing requirements of the splice must be met.

The seismic provisions must be reviewed carefully as splices require seismic detailing even when the column is not considered to be part of the seismic force resisting system. Some of the seismic detailing requirements for splices include minimum horizontal shear capacity, locations of the splices relative to the building diaphragms, and verification that the columns above and below the splice meet the seismic compactness requirements.

Refer to AISC for all seismic detailing requirements. The end plate column splice is simple to design, detail and construct, thus it is likely one of the most economical splice options. The splice consists of welding an end plate with bolt holes onto the ends of both the upper and lower column sections.

The erection time in the field is minimal since only bolts are required to fasten the splice together. For a pinned splice, the end plates and bolts can be chosen as nominal sizes as long as they are adequate for shear forces that may be present. The main drawback to the end plate splice is that since the plates extend beyond the faces of the HSS column, it may not fit within the architectural aesthetic requirements or may interfere with the installation of cladding elements.

The side plate splice makes use of direct bearing of the upper column on the lower column to transfer the axial compression. The side plates at the column walls transfer the remaining loads and serve as guides to ensure alignment, therefore, column segments on each side of the splice must have the same nominal size.

The side plates are shop attached to the lower column with either welds or bolts and can be located on either the inside or outside of the column walls.

The upper column is attached to the side plates in the field with either bolts or fillet welds. The field bolting option is limited because standard bolt installation requires access to both sides of the bolt which in this case is not possible.

Therefore, proprietary blind bolts must be used which allow installation with access to one side only. The transfer of axial compression from the upper to lower column segments appears to be straight forward, especially with the alignment plates ensuring direct bearing. However, the intricacies in the geometry of the HSS section warrant a closer look at the bearing strength. The bearing area becomes critical when the two column segments have different thicknesses because the corner bending radius in HSS sections varies based on the thickness.

A thin HSS section has a small corner radius which means that when it is sitting on a thicker HSS section with a larger corner it is possible that the corners of the thinner section may extend beyond the thicker column. Since the corners do not align, the actual bearing area is less than the area of the full HSS section and must be checked closely.

Perhaps the easiest splice to design is the direct welded splice, however, it may also be the most expensive splice option. As with the side plate, the axial compression is transmitted through direct bearing of the column ends.

Using a complete joint penetration CJP weld will provide the strongest splice resulting in full moment capacity of the HSS section. However, there are three major drawbacks to detailing a CJP welded splice.Log In. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.

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where should splices in column be provided

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Hey guys, do you have any best idea about field weld splice connection for HSS column, also advise how to calculate its full splice capacity, suggestions that may conclude CISC would be best. Thanks in advance!!

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Its hard to say what the "best" weld detail may be for your situation without a little more detail. Do you need the splice to develop full capacity? Are there any access or any other restrictions? What size HSS? The simplest to detail though not the simplest to perform would be a full pen weld with backing bar inside the HSS.

Another option would be a cap plate welded between the 2 sections - this could be shop fabricated on the bottom section and field welded to the top section. The cap plate with fillet welds would be the cheapest to fabricate.

Quote dauwerda. By full capacity do you mean full axial capacity or full moment capacity? If this column is strictly axial and has negligible moment demand there is typically no need to use a full pen weld as the axial capacity is developed through bearing. In welding tube steel, backing bars can't be used practically and backgouging isn't possible.

So, the trick is to use butt plate.This however cannot be accomplished for practical reasons therefore, the length of the longitudinal rebars is equal to the height of each storey. When lapping steel bars from successive stories, it is important to ensure the correct transmission of forces from the rebars of the superjacent floor to the rebars of the subjacent floor.

This can be achieved by welding, however this method has a number of technical difficulties and it is used only in special occasions. The practice usually followed is the rebar lap-splicing i. It is important to thoroughly understand how the lap-splices are being done in practice. One must always keep in mind that in order for the stirrups to provide confinement, every rebar must be placed inside one of their corners.

This however is difficult to be done at the beginning and at the end of the lap-splice and it can be achieved only with special practices. In case the rebars are wired together on the site, the lap-splice is mandatory to be done according to the first way shown at the opposite figure. The starter bars of the subjacent storey must be kept straight while the rebars of the above floor must be bent at their joint point.

The bent part must extend to one or two stirrups. The following table shows the necessary lap lengths in mm, for three different rebar diameters in combination with three different concrete grades.

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The bent rebars can be placed in contact with the straight ones in any direction as shown at the following figures. In case there are no seismic design requirements and for serviceability reasons, it is preferred to place more bars with smaller diameter around the perimeter instead of fewer bars with larger diameter.

When seismic design is required, as it is for the columns referred in this book, it is preferred to place rebars only inside the corners of the stirrups thus ensuring that no buckling will occur. Therefore, it is better to use fewer bars with larger diameter. Moreover, structures designed to withstand the seismic hazard, have a considerable amount of steel reinforcement in their joint areas so the small number of column rebars enables the proper reinforcement. The first condition regards the concrete industry while the second and third regard the formation and placement of the reinforcing steel.

The latter two conditions are discussed further below. In a highly seismically active country such as Greece, the usage of high concrete strength classes is not only more economical but technically mandatory.

The construction industrialization together with the development of the reinforcement implemen-tation, is contributing to the growing use of prefabricated stirrup cages and also to the use of prefabricated columns that are positioned with the use of a crane.

The prefabricated reinforcement and its mechanical implementation are two simultane-ously developing techniques. Earthquake resistant columns have a large mass. For instance, the smallest allowable column mentioned before stirrups and longitudinal reinforcementhas a mass equal to 60 kg as op-posed to the usual antiseismic columns whose mass is much greater. You are commenting using your WordPress. You are commenting using your Google account.

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Notify me of new comments via email. Notify me of new posts via email. Skip to content. Home About. Figure 4.Lap Length is required when bars placed short of their required length due to nonavailability of longer bars need to be extended.

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This invariably introduces stress concentrations at this surrounding concrete. These effects should be minimized by. When splicing in such situations becomes unavoidable, special precautions need to be employed, such as.

Lap splices are achieved by overlapping this bars over a certain length, thereby enabling this transfer of axial force from the terminating bar into the connecting bar through the mechanism of anchorage development bond with the surrounding concrete As per below fig. The splitting and cracking behavior observed in lap splice tests are found to be similar to those in anchorage bond tests As per below fig.

B Use of spirals in lap splices for large diameter bars. The Lap splices are usually not permitted for very large dia. It is desirable to bend the bars slightly particularly large diameter bars near the splice location in order to ensure a collinear transfer of force without eccentricityas shown above, fig A. As the force transfer is through development bond, the lap length should at least be equal to the development length Ld.

When bars of two different diameters are to be spliced, the lap length should be calculated on the basis of the smaller diameter. Splices in tension members shall be enclosed in spirals made of bars not less than 6 mm diameter with the pitch, not more than 10mm. When lapping of tension reinforcement is required in the top of a beam usually near a continuous support location or a beam-column junctionand the clear cover is less than twice the diameter of the lapped bar, the lapped length should be increased by a factor of 1.

If the rebar is required into turn around a corner as in an exterior beam-column junctionthe lapped length should be increased by a factor of 2. This factor can be limited to 1. When more than one bar requires splicing, care must be taken to ensure that the splicing is staggered, with a minimum center-to-center separation of 1. It is also desirable to provide extra transverse ties especially in columnsconnecting the various longitudinal bars in the spliced region.

In the case of bundled bars, the lap length should be calculated considering the increased Ldand the individual splices within a bundle should be staggered. Welded splices and mechanical connections are particularly suitable for large diameter bars. This results in reduced consumption of reinforcing steel. It is desirable to subject such splices to tension tests in order to ensure the adequacy of strength.

Welding of cold-worked bars needs special precautions owing to the possibility of a loss in strength on account of welding heat. Butt welding of bars is generally adopted in welded splices.Consider a column with cross section x This is the smallest allowable column section when seismic behavior is required.

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It is reinforced with 4 longitudinal bars and one stirrup. The cross section described is not generally used but it was chosen in this introductory paragraph for training purposes. The column has a length of 2. The shear reinforcement can be referred to with various names such as stirrups, ties, hoop reinforcement etc. Columns are the most critical structural components to ensure the required seismic perform-ance of the building and the shear reinforcement is the most critical component of the columns.

In every column we define areas with high ductility demand when earthquake loads are ap-plied which they are called critical, areas with lower ductility demand, called non-critical and the joint area i. The hooks of the shear reinforcement should be formed in different positions along the perime-ter of the stirrups in each layer but due to the frequent use of industrial stirrup cages this is not feasible.

Columns Consider a column with cross section x Note The hooks of the shear reinforcement should be formed in different positions along the perime-ter of the stirrups in each layer but due to the frequent use of industrial stirrup cages this is not feasible.Lap length is one of the important term in the reinforcement. This is usually confused with another important term called development length and anchorage length.

In this article, the lap lengths of bars is discussed. During the placement of steel in Reinforced concrete structureif the required length of single bar may fall short. To get the desired design length, lapping of two bars side by side is done. An alternative to this is to provide mechanical couplers.

Lapping can be defined as the overlapping of two bars side by side to upto the design length. Usually, the stock length of steel bars is limited to 12m.

where should splices in column be provided

This is for easy transportation of steel bars to the construction site. For example, imagine there is a need to build a ft tall column. Hence the bars are cut every second story. Then the tension forces are required to be transferred from one bar to the other bar at the location of discontinuity of the bar. So the second bar is kept closely to the first bar and overlapping is done. Lapping is usually done where minimum bending stress is encountered.

In general, lap length is 50d which means 50 times the bar diameter, if both bars are of same diameter. The lap length is equal to the development length calculated in compression but not less than 24d. When the bars of different diameters are to be spliced, the lap length is calculated considering the smaller diameter bar.

Lap splices should not be catered for the bars which are having diameter greater than 36 mm. In such cases, welding should be considered. But if welding is also not feasible in some conditions, then lapping may be allowed for the bars larger than 36 mm diameter. But along with lapping, additional spirals of 6 mm should be provided around the lapped bars. The Lapping length in tension MS bar — mild steel bar including anchorage value is 58d.

Lap length in Reinforced Concrete Lap length is one of the important term in the reinforcement.Details shall be as shown in the BDM. Welded laps are used for splicing and terminating spirals, BDM fig. The single sided weld has been used exclusively in construction and is preferred. The double sided weld detail should be removed in future plans.

Avoid bundled spirals where both bars are required to terminate at the same location four bars stacked at the lap weld. Where hoops are required for columns, they shall be shop fabricated using either a manual direct butt weld per AWS D1.

Ultimate couplers, as defined by Caltrans specifications, may be considered provided cover and clearance requirements are accounted for. A list of potential couplers is shown below. Some ultimate couplers are currently listed on the QPL. Otherwise, hoops of sizes 7 through 9 may be used.

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Welded lap splices for shaft hoops shown in the BDM, Figure 7. The single sided weld is preferred. Hoops for shafts shall be shop fabricated or field welded before installation in the shaft cage. A number of ultimate couplers are suitable for field installation with the shaft cage. Only manual welded splices and mechanical couplers are covered by the Standard Specifications. This requirement is not currently covered by the Standard Specification.

Where hoops or ultimate couplers are used, the plans should show a staggered splice placement pattern. Where interlocking hoops are used, the splices should be located in the column interior. Potential List of Ultimate Couplers for Hoops:. Headed Reinforcement Corp.