Scrapers ~ these machines consist of a scraper bowl which is lowered to cut and collect soil where site stripping and levelling operations are required involving large volume of earth.
When the scraper bowl is full the apron at the cutting edge is closed to retain the earth and the bowl is raised for travelling to the disposal area. On arrival the bowl is lowered, the apron opened and the spoil pushed out by the tailgate as the machine moves forwards.
Scrapers are available in three basic formats:
1. Towed Scrapers † these consist of a four wheeled scraper bowl which is towed behind a power unit such as a crawler tractor. They tend to be slower than other forms of scraper but are useful for small capacities with haul distances up to 300.
2. Two Axle Scrapers † these have a two wheeled scraper bowl with an attached two wheeled power unit. They are very manoeuvrable with a low rolling resistance and very good traction.
3. Three Axle Scrapers † these consist of a two wheeled scraper bowl which may have a rear engine to assist the four wheeled traction engine which makes up the complement.
Generally these machines have a greater capacity potential than their counterparts, are easier to control and have a faster cycle time.
To obtain maximum efficiency scrapers should operate downhill if possible, have smooth haul roads, hard surfaces broken up before scraping and be assisted over the last few metres by a pushing vehicle such as a bulldozer.
Typical Scraper Details
Common constructions that require some kind of underwater exploration program include bridge piers, port structures, pipelines, oil well platforms, land recovery (fills to extend the shore line or for an island), and the like. It is usually necessary to collect enough data to make a strength estimate.
Soil shear strength determines how much pile embedment is required or whether a fill will require special construction procedures. Estimates of settlement are also often required—both how much and how long it will take. This is very critical for land recovery operations, since the client will want to know when enough settlement has occurred so that construction of surface facilities can begin.
The in situ testing and recovery procedures for underwater samples, either in a freshwater or a saltwater environment, are not much different from those for dry land for water depths up to about 45 m. The principal differences are that the testing or drilling equipment is mounted on a barge that is towed to the test location and securely anchored and that casing is used, at least to the water bed and possibly 1 or 2 meters into the bed.
The casing strength is the principal cause for limiting the depth to about 45 m. For this situation the barge is securely anchored using four to six anchors so it does not shift or twist. Sometimes divers are used to observe visually if any construction difficulty will be encountered or if there are any existing underwater obstructions.
A barge-mounted drilling rig (drilling over the side) is a common method for drilling in rivers, in lake beds, and in the shallower water along the continental shelf for bridges, port structures, or land recovery. Penetration, vane, and pressuremeter tests described in the following sections can be made in the borings.
In deeper water (up to 1,000+ m) wave action requires alternative exploration equipment, such as a small ship converted to a drilling platform by installing a center well of 460 to 610 mm diameter from the deck through the hull and adding a drill rig. This configuration is sometimes called a drill ship.
Submarine-type vessels (sometimes called submersibles) are also used. In very deep water a platform might be constructed, off of which the exploration crew might work. Any of these equipment options will allow recovery of samples of reasonable quality.
Where wave action occurs, it is necessary to use casing with flexible joints, and a casing diameter large enough to allow passage of the sampling (or test device) tube. In deeper water the drill pipe may act as the casing (again using flexible joints). In this case the lower end of the pipe holds the auger bit, which produces an over-sized hole.
At the desired level a sampler is lowered through the drill pipe to the base of the hole and either driven or pushed into the soil below the bit.
There are also projectile-type devices that are lowered to the ocean floor from the drill ship to recover soil samples. Servomechanisms commanded from the surface may be used to force a sample tube into the soil using the weight of either the surface vessel or some kind of reaction device placed on the seafloor.
A projectile device may contain a gas or explosive charge to propel a sample tube into the soil, again using the weight of the total device as a reaction. Most of these types of devices are patented and/or proprietary. Deepwater divers are sometimes used to recover samples or to inspect the reaction device.
In situ tests are currently considered preferable to sample recovery, particularly for strength testing. It is difficult to recover good-quality samples from underwater because of the change in pore pressure when the sample is brought above water. As a minimum, air bubbles tend to come out of the pore water and occupy a greater volume, causing the sample to expand or even explode.
If the sample is still in the sample tube, the expansion may cause the sample to extend out of the tube end(s). Depending on the equipment, the sample recovery tube (about 50- to 75-mm ID and 610 to 100O+ mm in length) may be pushed or driven.
A pushed sample is generally of better quality than one obtained by driving the tube into the soil. Shorter tube lengths generally produce better-quality samples, since side friction is significant with all tube samples; if the sample is too long, it may become compressed from side friction between the sample and the inside walls of the sampler.
At a given site a few samples should be recovered for visual inspection and possibly some index tests (w#, W>L, Ip). A driven-tube recovered sample will often have excessive disturbance for strength testing, but the blow count to drive the tube gives some indication of soil strength, somewhat like the SPT test described in the next section.
A number of underwater exploration methods are described in ASTM (1971) and appear among the references cited by Focht and Kraft (1977), which the interested reader may wish to consult. Using the in situ vane test for underwater exploration is described in ASTM (1988). Olsen et al. (1986) described an elaborate marine sampling and testing program undertaken in 1979-1980.
Natural Cementation and Aging
All soils undergo a natural cementation at the particle contact points. The process of aging seems to increase the cementing effect by a variable amount. This effect was recognized very early in cohesive soils but is now deemed of considerable importance in cohesionless deposits as well.
The effect of cementation and aging in sand is not nearly so pronounced as for clay but still the effect as a statistical accumulation from a very large number of grain contacts can be of significance for designing a foundation.
A soil is said to be normally consolidated (nc) if the current overburden pressure (column of soil overlying the plane of consideration) is the largest to which the mass has ever been subjected. It has been found by experience that prior stresses on a soil element produce an imprint or stress history that is retained by the soil structure until a new stress state exceeds the maximum previous one. The soil is said to be overconsolidated (or preconsolidated) if the stress history involves a stress state larger than the present overburden pressure.
Mode of Deposit Formation
Soil deposits that have been transported, particularly via water, tend to be made up of small grain sizes and initially to be somewhat loose with large void ratios. They tend to be fairly uniform in composition but may be stratified with alternating very fine material and thin sand seams, the sand being transported and deposited during high-water periods when stream velocity can support larger grain sizes. These deposits tend to stabilize and may become very compact (dense) over geological periods from subsequent overburden pressure as well as cementing and aging processes.
Quality of the Clay
The term clay is commonly used to describe any cohesive soil deposit with sufficient clay minerals present that drying produces shrinkage with the formation of cracks or fissures such that block slippage can occur. Where drying has produced shrinkage cracks in the deposit we have a fissured clay.
This material can be troublesome for field sampling because the material may be very hard, and fissures make sample recovery difficult. In laboratory strength tests the fissures can define failure planes and produce fictitiously low strength predictions (alternatively, testing intact pieces produces too high a prediction) compared to in situ tests where size effects may either bridge or confine the discontinuity.
Soil water may be a geological phenomenon; however, it can also be as recent as the latest rainfall or broken water pipe. An increase in water content tends to decrease the shear strength of cohesive soils. An increase in the pore pressure in any soil will reduce the shear strength.
A sufficient increase can reduce the shear strength to zero—for cohesionless soils the end result is a viscous fluid. A saturated sand in a loose state can, from a sudden shock, also become a viscous fluid. This phenomenon is termed liquefaction and is of considerable importance when considering major structures (such as power plants) in earthquake-prone areas.
Steel sheet piling is used in many types of temporary works and permanent structures. The sections are designed to provide the maximum strength and durability at the lowest possible weight consistent with good driving qualities. The design of the section interlocks facilitates pitching and driving and results in a continuous wall with a series of closely fitting joints.
A comprehensive range of sections in both Z and U forms with a wide range of sizes and weights is obtainable in various different grades of steel which enables the most economic choice to be made to suit the nature and requirements of any given contract.
For applications where corrosion is an issue, sections with minimum thickness can be delivered to maximise the effective life of the structure. The usual requirements for minimum overall thickness of 10 mm, 12 mm or 1/2 inch can be met. Corner and junction piles are available to suit all requirements.
River control structures and flood defence
Steel sheet piling has traditionally been used for the support and protection of river banks, lock and sluice construction, and flood protection. Ease of use, length of life and the ability to be driven through water make piles the obvious choice.
Ports and harbours
Steel sheet piling is a tried and tested material to construct quay walls speedily and economically. Steel sheet piles can be designed to cater for heavy vertical loads and large bending moments.
Historically used as temporary support for the construction of pumping stations, sheet piling can be easily designed as the permanent structure with substantial savings in time and cost. Although pumping stations tend to be rectangular, circular construction should be considered as advantages can be gained from the resulting open structure.
Abutments formed from sheet piles are most cost effective in situations when a piled foundation is required to support the bridge or where speed of construction is critical. Sheet piling can act as both foundation and abutment and can be driven in a single operation, requiring a minimum of space and time for construction.
Road widening retaining wallsKey requirements in road widening include minimised land take and speed of construction particularly in lane rental situations. Steel sheet piling provides these and eliminates the need for soil excavation and disposal.
Labels: Steel Works
The Unified Soil Classification System is based on the airfield classification system developed by A. Casagrande during World War II. With some modification it was jointly adopted by several U.S. government agencies in 1952. Additional refinements were made and it is currently standardized as ASTM D 2487-93. It is used in the U.S. and much of the world for geotechnical work other than roads and highways.
In the unified system soils are designated by a two-letter symbol: the first identifies the primary component of the soil, and the second describes its grain size or plasticity characteristics. For example, a poorly graded sand is designated SP and a low plasticity clay is CL. Five first-letter symbols are used:
G for gravel
S for sand
M for silt
C for clay
O for organic soil
Clean sands and gravels (having less than 5% passing the No. 200 sieve) are given a second letter P if poorly graded or W if well graded. Sands and gravels with more than 12% by weight passing the No. 200 sieve are given a second letter M if the fines are silty or C if fines are clayey.
Sands and gravels having between 5 and 12% are given dual classifications such as SP-SM. Silts, clays, and organic soils are given the second letter H or L to designate high or low plasticity. The specific rules for classification are summarized as follows and described in detail in ASTM D 2487.
Organic soils are distinguished by a dark-brown to black color, an organic odor, and visible fibrous matter. For soils that are not notably organic the first step in classification is to consider the percentage passing the No. 200 sieve.
If less than 50% of the soil passes the No. 200 sieve, the soil is coarse grained, and the first letter will be G or S; if more than 50% passes the No. 200 sieve, the soil is fine grained and the first letter will be M or C.
For coarse-grained soils, the proportions of sand and gravel in the coarse fraction (not the total sample) determine the first letter of the classification symbol. The coarse fraction is that portion of the total sample retained on a No. 200 sieve.
Atterberg limits, named after the Swedish soil scientist A. Atterberg, are water content values at which notable changes in soil behavior occur. The liquid limit , denoted LL or wL, marks the transition between liquid and plastic behavior.
At water contents above the liquid limit the soil behaves as a viscous liquid; below the liquid limit the soil behaves as a plastic solid. The liquid limit is determined in the laboratory by partly filling a standard brass cup with wet soil and cutting a groove of a standard dimension in the soil.
The liquid limit is taken as the water content at which the groove closes a specified amount when the cup is lifted and dropped 1 cm exactly 25 times. The details of the test are given in AASHTO T 89 and ASTM D 4318-93.
The plastic limit, denoted PL or wp, is the transition between plastic and brittle behavior. It is determined in the laboratory as the water content at which a 1/8-inch diameter thread of soil begins to crumble when rolled under the palm of the hand.
Details of the liquid limit and plastic limit tests are provided by AASHTO T 90 and ASTM D 4318-93. The shrinkage limit, denoted SL or wS, is the water content below which the soil no longer reduces in volume when the water content is reduced.
Although Atterberg limits are water contents and are properly decimals or percentages, they are usually expressed as an integer percentage without a percent sign. Thus, a liquid limit of 40% is usually reported as LL = 40.
The plasticity index, denoted PI or IP, is the difference of the liquid limit and the plastic limit:
PI = LL – PL
The liquidity index, denoted LI or IL , is a measure of the natural water content (w) relative to the plastic limit and the liquid limit:
Large-grained materials such as cobbles and boulders are sometimes considered to be soil. The differentiation of cobbles and boulders depends somewhat on local practice, but boulders are generally taken to be particles larger than 200 to 300 mm or 9 to 12 in.
The Unified Soil Classification System suggests that boulders be defined as particles that will not pass a 12-in. (300 mm) opening. Cobbles are smaller than boulders and range down to particles that are retained on a 3-inch (75 mm) sieve.
Gravels and sands are classified as coarse-grained soils; silts and clays are fine-grained soils. For engineering purposes, gravel is defined as soil that passes a 3-inch (75 mm) sieve and is retained by a No. 4 sieve (4.75 mm or 0.187 in.) or No. 10 sieve (2.00 mm or 0.078 in.), depending on the classification system.
Sand is defined as soil particles smaller than gravel but retained on a No. 200 sieve (0.075 mm or about 0.003 in.). Soils passing the No. 200 sieve may be silt or clay. Although grain-size criteria were used in some older classification systems to differentiate silt from clay, the two systems described herein make this differentiation based on plasticity rather than grain size.
Opening sizes of commonly used sieves are shown in Table 15.1.
A sample of dry soil is poured onto the top sieve, the nest is covered, and it is then shaken by hand or mechanical shaker until each particle has dropped to a sieve with openings too small to pass, and the particle is retained.
The cumulative weight of all material larger than each sieve size is determined and divided by the total sample weight to obtain the percent retained for that sieve size, and this value is subtracted from 100% to obtain the percent passing that sieve size.
Results are displayed by plotting the percent passing (on a linear scale) against the sieve opening size (on a log scale) and connecting the plotted points with a smooth curve referred to as a grain-size distribution curve.
Green-Field † land not previously built upon. Usually part of the `green†belt' surrounding urban areas, designated inappropriate for development in order to preserve the countryside. Limited development for agricultural purposes only may be permitted on `green-belt' land.
Brown-Field † derelict land formerly a developed site and usually associated with previous construction of industrial buildings. UK government has set an objective to build 60% of the 4 million new homes required by 2016 on these sites.
Site Survey † essential that a geo†technical survey is undertaken to determine whether contaminants are in the soil and ground water. Of particular concern are: acids, salts, heavy metals, cyanides and coal tars, in addition to organic materials which decompose to form the highly explosive gas, methane.
Analysis of the soil will determine a `trigger threshold value', above which it will be declared sensitive to the end user. For example, a domestic garden or children's play area will have a low value relative to land designated for a commercial car park.
Site Preparation † when building on sites previously infilled with uncontaminated material, a reinforced raft type foundation may be adequate for light structures. Larger buildings will justify soil consolidation and compaction processes to improve the bearing capacity. Remedial measures for subsoils containing chemicals or other contaminants are varied.
Legislation † the Environment Protection Act of 1990 attempted to enforce responsibility on local authorities to compile a register of all potentially contaminated land. This proved unrealistic and too costly due to inherent complexities.
Caissons are box-like structures which are similar in concept to cofferdams but they usually form an integral part of the finished structure. They can be economically constructed and installed in water or soil where the depth exceeds 18„000.
There are 4 basic types of caisson namely:
1 . Box Caissons
2. Open Caissons
3. Monolithic Caissons
4. Pneumatic Caissons
Pneumatic Caissons ~ these are sometimes called compressed air caissons and are similar in concept to open caissons. They can be used in difficult subsoil conditions below water level and have a pressurised lower working chamber to provide a safe dry working area.
Underpinning ~ the main objective of most underpinning work is to transfer the load carried by a foundation from its existing bearing level to a new level at a lower depth. Underpinning techniques can also be used to replace an existing weak foundation. An underpinning operation may be necessary for one or more of the following reasons:-
1. Uneven Settlement † this could be caused by uneven loading of the building, unequal resistance of the soil action of tree roots or cohesive soil settlement.
2. Increase in Loading † this could be due to the addition of an extra storey or an increase in imposed loadings such as that which may occur with a change of use.
3. Lowering of Adjacent Ground † usually required when constructing a basement adjacent to existing foundations.
General Precautions ~ before any form of underpinning work is commenced the following precautions should be taken:-
1. Notify adjoining owners of proposed works giving full details and temporary shoring or tying.
2. Carry out a detailed survey of the site, the building to be underpinned and of any other adjoining or adjacent building or structures. A careful record of any defects found should be made and where possible agreed with the adjoining owner(s) before being lodged in a safe place.
3. Indicators or `tell tales' should be fixed over existing cracks so that any subsequent movements can be noted and monitored.
4. If settlement is the reason for the underpinning works a thorough investigation should be carried out to establish the cause and any necessary remedial work put in hand before any underpinning works are started.
5. Before any underpinning work is started the loads on the building to be underpinned should be reduced as much as possible by removing the imposed loads from the floors and installing any props and/or shoring which is required.
Site Analysis † prior to purchasing a building site it is essential to conduct a thorough survey to ascertain whether the site characteristics suit the development concept. The following guidance forms a basic checklist:
* Refer to Ordnance Survey maps to determine adjacent features, location, roads, facilities, footpaths and rights of way.
* Conduct a measurement survey to establish site dimensions and levels.
* Observe surface characteristics, i.e. trees, steep slopes, existing buildings, rock outcrops, wells.
* Inquire of local authority whether preservation orders affect the site and if it forms part of a conservation area.
* Investigate subsoil. Use trial holes and borings to determine soil quality and water table level.
* Consider flood potential, possibilities for drainage of water table, capping of springs, filling of ponds, diversion of streams and rivers.
* Consult local utilities providers for underground and overhead services, proximity to site and whether they cross the site.
* Note suspicious factors such as filled ground, cracks in the ground, subsidence due to mining and any cracks in existing buildings.
* Regard neighbourhood scale and character of buildings with respect to proposed new development.
* Decide on best location for building (if space permits) with regard to `cut and fill', land slope, exposure to sun and prevailing conditions, practical use and access.
Site Investigation For New Works ~ the basic objective of this form of site investigation is to collect systematically and record all the necessary data which will be needed or will help in the design and construction processes of the proposed work.
Correct application of materials produced to the recommendations of British, European and International Standards authorities, in accordance with local building regulations, by-laws and the rules of building guarantee companies, i.e. National House Building Council (NHBC) and MD Insurance
Services, should ensure a sound and functional structure. However, these controls can be seriously undermined if the human factor of quality workmanship is not fulfilled. The following guidance is designed to promote quality controls:
BS 8000: Workmanship on building sites.
Building Regulations, Approved Document to support Regulation 7
† materials and workmanship.
No matter how good the materials, the workmanship and supervision, the unforeseen may still affect a building. This may materialise several years after construction. Some examples of these latent defects include: woodworm emerging from untreated timber, electrolytic decomposition of dissimilar metals inadvertently in contact, and chemical decomposition of concrete.
Generally, the older a building the more opportunity there is for its components and systems to have deteriorated and malfunctioned.
Hence the need for regular inspection and maintenance. The profession of facilities management has evolved for this purpose and is represented by the British Institute of Facilities Management (BIFM).
Property values, repairs and replacements are of sufficient magnitude for potential purchasers to engage the professional services of a building surveyor. Surveyors are usually members of the Royal Institution of Chartered Surveyors (RICS).
The extent of survey can vary, depending on a client's requirements. This may be no more than a market valuation to secure financial backing, to a full structural survey incorporating specialist reports on electrical installations, drains, heating systems, etc.
Further reading: BRE Digest No. 268 † Common defects in low-rise traditional housing. Available from Building Research Establishment Bookshop † www.brebookshop.com.
The reduced beam section shall be made using thermal cutting to produce a smooth curve. The maximum surface roughness of the thermally cut surface shall be 500 microinches (13 microns) in accordance with ANSI B46.1, as measured using AWS C4.1–77 Sample 4 or similar visual comparator.
All transitions between the reduced beam section and the unmodified beam flange shall be rounded in the direction of the flange length to minimize notch effects due to abrupt transitions. Corners between the reduced section surface and the top and bottom of the flanges shall be ground to remove sharp edges, but a minimum chamfer or radius is not required.
Thermal cutting tolerances shall be plus or minus 1/4 in. (6 mm) from the theoretical cut line. The beam effective flange width at any section shall have a tolerance of plus or minus 3/8 in. (10 mm).
Gouges and notches that occur in the thermally cut RBS surface may be repaired by grinding if not more than 1/4 in. (6 mm) deep. The gouged or notched area shall be faired by grinding so that a smooth transition exists, and the total length of the area ground for the transition shall be no less than five times the depth of the removed gouge on each side of the gouge.
If a sharp notch exists, the area shall be inspected by MT after grinding to ensure that the entire depth of notch has been removed. Grinding that increases the depth of the RBS cut more than 1/4 in. (6 mm) beyond the specified depth of cut is not permitted.
Gouges and notches that exceed 1/4 in. (6 mm) in depth, but not to exceed 1/2 in. (12 mm) in depth, and those notches and gouges where repair by grinding would increase the effective depth of the RBS cut beyond tolerance, may be repaired by welding. The notch or gouge shall be removed and ground to provide a smooth radius of not less than 1/4 in. in preparation for welding.
Columns shall satisfy the following limitations:
(1) Columns shall be any of the rolled shapes or built-up sections permitted in Section 2.3 of AISC.
(2) The beam shall be connected to the flange of the column.
(3) Rolled shape column depth shall be limited to W36 (W920). The depth of built-up wide-flange columns shall not exceed that for rolled shapes.
Flanged cruciform columns shall not have a width or depth greater than the depth allowed for rolled shapes. Built-up box columns shall not have a width or depth exceeding 24 in. (610 mm). Boxed wide flange columns shall not have a width or depth exceeding 24 in. (610 mm) if participating in orthogonal moment frames.
(4) There is no limit on the weight per foot of columns.
(5) There are no additional requirements for flange thickness.
(6) Width-thickness ratios for the flanges and web of columns shall conform to the limits in Table I–8–1 of the AISC Seismic Provisions.
Beams shall satisfy the following limitations:
(1) Beams shall be rolled wide-flange or built-up I-shaped members conforming to the requirements of Section 2.3 of AISC.
(2) Beam depth is limited to W36 (W920) for rolled shapes. Depth of built-up sections shall not exceed the depth permitted for rolled wide-flange shapes.
(3) Beam weight is limited to 300 lbs/ft (447 kg/m).
(4) Beam flange thickness is limited to 13/4 in. (44.5 mm).
(5) The clear span-to-depth ratio of the beam shall be limited as follows:
(a) For SMF systems, 7 or greater.
(b) For IMF systems, 5 or greater.
(6) Width-thickness ratios for the flanges and web of the beam shall conform to the limits of the AISC Seismic Provisions. When determining the width-thickness ratio of the flange, the value of bf shall not be taken as less than the flange width at the ends of the center two-thirds of the reduced section provided that gravity loads do not shift the location of the plastic hinge a significant distance from the center of the reduced beam section.
(7) Lateral bracing of beams shall be provided as follows:
(a) For SMF systems, in conformance with Section 9.8 of the AISC Seismic Provisions. Supplemental lateral bracing shall be provided at the reduced section in conformance with Section 9.8 of the AISC Seismic Provisions for lateral bracing provided adjacent to the plastic hinges.
References to the tested assembly in Section 9.8 of the AISC Seismic Provisions do not apply. When supplemental lateral bracing is provided, attachment of supplemental lateral bracing to the beam shall be located no greater than d/2 beyond the end of the reduced beam section farthest from the face of the column, where d is the depth of the beam.
No attachment of lateral bracing shall be made to the beam in the region extending from the face of the column to end of the reduced section farthest from the face of the column. (b) For IMF systems, in conformance with Section 10.8 of the AISC Seismic Provisions.
Exception: For both systems, where the beam supports a concrete structural slab that is connected between the protected zones with welded shear connectors spaced a maximum of 12 in. (300 mm) on center, supplemental top and bottom flange bracing at the reduced section is not required.
Continuity Plate Thickness
Where continuity plates are required, the thickness of the plates shall be determined as follows:
(a) For one-sided (exterior) connections, continuity plate thickness shall be at least one-half of the thickness of the beam flange.
(b) For two-sided (interior) connections, the continuity plate thickness shall be at least equal to the thicker of the two beam flanges on either side of the column. Continuity plates shall also conform to the requirements of Section J10 of the AISC Specification.
Continuity Plate to Column Attachment
Continuity plates, if provided, shall be welded to column flanges using CJP groove welds. Continuity plates shall be welded to column webs using groove welds or fillet welds.
The required strength of the sum of the welded joints of the continuity plates to the column web shall be the smallest of the following:
(a) The sum of the design strengths in tension of the contact areas of the continuity plates to the column flanges that have attached beam flanges.
(b) The design strength in shear of the contact area of the plate with the column web.
(c) The design strength in shear of the column panel zone.
(d) The sum of the expected yield strengths of the beam flanges transmitting force to the continuity plates.
Continuity Plates Welding
Along the web, the corner clip shall be detailed so that the clip extends a distance of at least 11/2 in. (38 mm) beyond the published “k” detail dimension for the rolled shape. Along the flange, the plate shall be clipped to avoid interference with the radius of the rolled shape and shall be detailed so that the clip does not exceed a distance of 1/2 in. (12 mm) beyond the published “k1” detail dimension.
The clip shall be detailed to facilitate suitable weld terminations for both the flange weld and the web weld. When a curved clip is used, it shall have a minimum radius of 1/2 in. (12 mm).
At the end of the weld adjacent to the column web/flange juncture, weld tabs for continuity plates shall not be used, except when permitted by the engineer of record. Unless specified to be removed by the engineer of record, weld tabs shall not be removed when used in this location.
Where continuity plate welds are made without weld tabs near the column fillet radius, weld layers shall be permitted to be transitioned at an angle of 0° to 45° measured from the vertical plane. The effective length of the weld shall be defined as that portion of the weld having full size. Non destructive testing (NDT) shall not be required on the tapered or transition portion of the weld not having full size.
Built-up columns shall satisfy the requirements of AISC Specification Section E6 except as modified in this Section. Transfer of all internal forces and stresses between elements of the built-up column shall be through welds.
1. I-Shaped Welded Columns
The elements of built-up I-shaped columns shall conform to the requirements of the AISC Seismic Provisions. Within a zone extending from 12 in. (300 mm) above the upper beam flange to 12 in. (300 mm) below the lower beam flange, unless specifically indicated in this Standard, the column webs and flanges shall be connected using CJP groove welds with a pair of reinforcing fillet welds. The minimum size of fillet welds shall be the lesser of 5/16 in. (8 mm) or the thickness of the column web.
2. Boxed Wide-Flange Columns
The wide-flange shape of a boxed wide-flange column shall conform to the requirements of the AISC Seismic Provisions. The width-to-thickness ratio (b/t) of plates used as flanges shall not exceed 0.6 SQRT(Es /Fy), where b shall be taken as not less than the clear distance between plates.
The width-to-thickness ratio (h/tw) of plates used only as webs shall conform to the provisions of Table I–8–1 of the AISC Seismic Provisions. Within a zone extending from 12 in. (300 mm) above the upper beam flange to 12 in. (300 mm) below the lower beam flange, flange and web plates of boxed wide-flange columns shall be joined by CJP groove welds. Outside this zone, plate elements shall be continuously connected by fillet or groove welds.
3. Built-up Box Columns
The width-to-thickness ratio (b/t) of plates used as flanges shall not exceed 0.6#Es /Fy #, where b shall be taken as not less than the clear distance between web plates.
The width-to-thickness ratio (h/tw) of plates used only as webs shall conform to the requirements of the AISC Seismic Provisions. Within a zone extending from 12 in. (300 mm) above the upper beam flange to 12 in. (300 mm) below the lower beam flange, flange and web plates of box columns shall be joined by CJP groove welds. Outside this zone, box column web and flange plates shall be continuously connected by fillet welds or groove welds.
4. Flanged Cruciform Columns
The elements of flanged cruciform columns, whether fabricated from rolled shapes or built up from plates, shall meet the requirements of the AISC Seismic Provisions.
User Note: For flanged cruciform columns, the provisions of AISC Specification Section E6 must be considered. Within a zone extending from 12 in. (300 mm) above the upper beam flange to 12 in. (300 mm) below the lower beam flange, the web of the tee-shaped sections shall be welded to the web of the continuous I-shaped section with CJP groove welds with a pair of reinforcing fillet welds.
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- ▼ Jul (17)