4-67 (D) Health and Safety Responsibility
In addition to Article 105 -11 and Sections 106 and 107, provide effective engineering and work practice controls to insure adequate protection. Before beginning work, certif y to the Engineer that all personnel involved with lead paint removal operations (including rigging and material handling personnel) are properly trained and understand the applicable parts of EPA , 40 CFR Part 745, OSHA Standards , 29 CFR Part 1910 and 29 CFR Part 1926 including any amendments in force at the time of this contract.
442-15 Measurement and Payment
When the contract ex clude s the item of Painting of Structural Steel , there will be no direct payment for the work covered by this section. When the contract includes the item of Painting of Structural Steel , all work covered by this section , except for shop painting, will be paid at the contract lump sum price for this item. Payment at the contract lump sum price for Approx . ____ Lbs. Structural Steel as provided in
Article 440 — 10 will be full compensation for the work of shop painting.
Repair or replacement of paint damaged by any cause will be incidental to the work of this section. These prices and payments will be full compensation for all items required to paint steel structures including , but not limited to, those items contained in Article 442 -1. Pollution Control will be paid as the contract lump sum price. When provided for in the contract, payment will be made under: Pay Item Pay Unit Painting of Structural Steel Lump Sum Pollution Control Lump Sum
450-1 Description
Furnish and install piles in accordance with the contract and accepted submittals. Provide steel and prestressed concrete piles and composite piles with both concrete and steel sections shown in the plan s. Drive and drill in piles and use pile tips and accessories as shown in the plan s. Galvanize, metallize, restrike, redrive, splice, cut off and build up piles and perform predrilling, spudding and high- strain dynamic pile testing (dynamic pile testing) as necessary or required. Define “pile embedment” as the required pile embedment in the cap or footing and “pile penetration” as the minimum required pile tip elevation or penetration into natural ground, whichever is deeper. Define “natural ground” as below the ground or mud line before constructing any embankments. Define “spudding” as driving or dropping a steel H -pile and then removing it. Define “dynamic pile testing” as high -strain dynamic pile testing. The estimated pile lengths shown in the plan s are sufficient for the minimum required pile embedment and penetration and are estimates of the pile lengths needed for required driving resistance. For prestressed concrete piles, u se estimated pile lengths for pile order lengths or the Engineer will p rovide pile order lengths based on testing prestressed concrete piles with the dynamic pile testing equipment . For bridges with staged construction and pile order lengths based on testing prestressed concrete piles with the dynamic pile testing equipment , order lengths for latter stages will not be provided until pile driving for the previous stage of construction is complete.
4-68 450-2 Materials
Refer to Division 10. Item Section Flowable Fill, Non -Excavatable 1000 -7 Neat Cement Grout, Type 1 1003 Portland Cement Concrete, Class A 1000 Reinforcing Steel 1070 Steel and Prestressed Concrete Piles 1084 -1 Steel Pipe Pile Plates 1072 For drilled -in piles, Class A concrete shall meet Article 1000 -3 except as modified herein. Provide concrete with a slump of 6 inches to 8 inches . Use an approved high- range water reducer to achieve this slump. For composite piles with both prestressed concrete and steel H -pile sections, use prestressed concrete piles and steel H -piles that meet Section 1084. Use steel pile points and splicers that are on the NCDOT APL .
450-3 Construction Methods
A.Handling and Storing Piles Handle, transport and store piles so piles are kept clean and undamaged. Do not use chains, cables or hooks that can damage or scar piles. Do not damage coatings on steel piles. When handling prestressed concrete piles, support and lift piles at pick -up points shown in the plan s. Protect steel piles from corrosion. Store piles horizontally above ground upon platform skids, or other supports, and keep free from st anding water, dirt, grease, vegetation and other foreign material.
B.Pile Installation If applicable, completely excavate for caps or footings before installing piles. If applicable and unless noted otherwise in the plan s, construct embankments to bottom of cap or footing elevations for a horizontal distance of 50 feet from any pile except where fill slopes are within 50 feet of a pile. Install pile s with the following tolerances:
1.Axial alignment within 1/4 in/ft of vertical or batter shown in the plans ,
2.Horizontal alignment within 3 inches of plan location , and
3.Pile embedment within 3 inches more and 2 inches less of the embedment shown in the plan s. If necessary, build up prestressed concrete piles or splice steel piles as shown in the plan s. Do not use more than 3 sections (2 splices) of steel piling per pile. Cut off piles at required elevations along a plane normal to the axis of the pile as necessary. Do not damage or spall piles when cutting off prestress ed concrete piles.
C.Pile Accessories When required, use pile accessories including pipe pile plates and steel pile points and splicers shown in the plan s. Steel pile points for steel pipe piles include pipe pile cutting shoes and conical points. Use "insi de fit" pipe pile cutting shoes, i.e., cutting shoes with an outside diameter equal to the pipe pile diameter. Use pipe pile plates with a diameter equal to the pipe pile diameter.
4-69 Attach steel pile points to steel piles in accordance with the manufacture r’s instructions
and approved welding procedures . Weld a minimum length of twice the flange width for steel H-piles. Use steel pile tips with prestressed concrete piles as shown in the plan s. Use steel pile splicers for splicing steel H-pile tips and com posite piles. Attach steel pile splicers in accordance with the manufacturer’s instructions and approved welding procedures .
D.Driven Piles Do not drive piles within 50 feet of CIP concrete until the concrete cures for at least 3 days. Do not use vibratory hammers to install prestressed concrete piles. When predrilling, spudding and installing the initial portions of steel piles with vibratory hammers, submit these pile installatio n methods with the proposed pile driving methods and equipment for acceptance. The Engineer will review and approve the spudding depth and H -pile size, predrilling depth and diameter and depth of pile installation with a vibratory hammer . When using vibratory hammers to install steel piles, drive at least the last 15 feet with an impact hammer . Limit driving stresses in accordance with the AASHTO LRFD Bridge Design Specifications . Use AASHTO driving stress limits for sever e corrosive environments when calcium nitrite corrosion inhibitor is required for prestressed concrete piles. If a tip elevation is noted in the plan s, drive steel and prestressed concrete piles to the minimum required driving resistance and tip elevation. Otherwise, drive steel and pre stressed concrete piles to the minimum required driving resistance and at least 10 feet into natural ground. D rive composite piles to the minimum required driving resistance and the prestressed concrete and steel H-pile sections to their respective minimu m required tip elevations noted in the plan s. Redrive piles raised or moved laterally due to driving adjacent piles. For initial drive of prestressed concrete piles below a depth of 10 ft or 20% of pile length, whichever is greater, drive each pile contin uously except to pause driving for one hour or less to change pile cushions and remove templates. Design and construct templates so prestressed concrete piles can be driven to pile cut -off without exceeding the one -hour time limit. When a prestressed con crete pile attains the required resistance and pile penetration, do not drive the pile any further to avoid cutting off the pile. If a prestressed concrete pile does not have the minimum required driving resistance when the pile head is 1 ft above pile cut -off, stop driving the pile. Protect coatings in an approved manner when driving coated steel piles through templates. Repair damaged galvanizing in accordance with Article 1076 -7.
1.Predrilling and Spudding Perform predrilling and spudding as noted in the plan s and in accordance with the accepted submittals. Predrill pile locations to elevations noted in the plan s or approved by the Engineer. When noted in the plan s and at the Contractor’s option, spudding may be u sed in stead of predrilling. Do not perform spudding below predrilling elevations noted in the plan s or approved by the Engineer. When noted in the plan s or predrilling in water or wetlands, use temporary steel casings that meet Subarticle 450 -3(E)(1), except use steel casings with inside diameter s no more than 2 inches larger than predrilling diameter s. Use temporary casings from at least 2 feet above the static water elevation or ground line, whichever is higher, to at least 5 feet below the ground or mud line. More than 5 feet embedment may be necessary if temporary casings are not stable or predrilling or spudding disturbs material outside casings. Perform predrilling and spudding s o spoils are minimized, large ground movements and voids below ground do not occur and piles can be driven to the required resistance
4-70 and pile penetration. Do not deposit spoils in water or wetlands. R emove all
temporary casings before driving piles.
2.Driving Equipment Submit the proposed pile driving methods and equipment ( pile driving equipment data form ) including the pile driving hammer, hammer cushion, pile helmet and cushion for all piles for acceptance by the Engineer in accordance with Article 105-2 at least 30 days before driving piles. Do not submit more than 2 pile driving hammers per pile type per submittal. All equipment is subject to satisfactory field performance. Drive piles with accepted driving equipment and operate pile driving hammers in accordance with the manufacturer’s recommendations. Use hammers that will not overstress piles and will attain the required driving resistance between 30 and 150 blows per foot . Use variable energy air, steam, hydraulic or open end di esel hammer s to drive piles. Closed end diesel hammers are not allowed. Operate air and steam hammers within 10% of the manufacturer's rated speed or a rate approved by the Engineer. Use a plant and equipment for air or steam hammers with sufficient capacity to maintain, under working conditions, the manufacturer’s recommended volume and pressure. Equip the plant and equipment with accurate pressure gauges that are easily accessible. Equip open- end (single acting) diesel hammers with a graduated scale (jump stick) extending above the ram cylinder, graduated rings or grooves on the ram or an electric sound activated remote measuring instrument to determine the hammer stroke during driving. Expose and inspect the hammer cushion prior to beginning any pile driving and periodically during pile driving on the project. Replace or repair any hammer cushion that is less than 25% of its original thickness. Hold pile heads in position with pile helmets that fit over pile heads and extend down the sides of piles a sufficient distance. Protect pile heads of prestressed concrete piles from direct impact with the helm et. Size the helmet so prestressed concrete p ile will not touch pile sides and will allow adequate pile cushion thickness to control driving stresses. Use pile cushions made of new pine plywood with a thickness of at least 6 inches . Provide a new pile cushion for each prestressed concrete pile. Re place pile cushions during driving when a cushion is compressed more than 50% of its original thickness , begins to smoke or burn , or as directed by the pile driving criteria .
3.Required Driving Resistance The Engineer will determine if the proposed pile driving methods and equipment are acceptable and will provide the blows per foot (or blows per inch) and equivalent set for the required driving resistance noted in the plans, i.e., “pile driving criteria” except for structures with dynamic pile testing . For structures with dynamic pile testing, provide pile driving criteria for any bents and end bents with piles in accordance with Subarticle 450 -3(F)(4). Stop driving piles if “refusal ” is reached. R efusal occurs at 240 blows per foot (20 blows per inch) or any equivalent set (maximum set of 1/2 inch in 10 blows) with the required stroke as per the pile driving criteria .
4.Restriking and Redriving Piles If piles do not attain the required resistance with the estimated or order lengths, the Engineer may require the Contractor to stop driving piles, wait and restrike or redrive piles to attain the required resistance. When the Engineer requires restrikes or redrives, the Engineer will determine the number of restrikes or redrives and the time
4-71 to wait after stopping driving and between restrikes and redrives. The time to wait
will range from 4 to 24 hours. Use the same pile driving methods, equipment and compressed pile cushion from the previous driving to restrike or redrive pile s. Do not use cold diesel hammer s for restrike s or redrive s. Warm up hammer s by applying at least 20 blows to a previously driven pile or timber mats on the ground.
E.Drilled -in Piles Perform pile excavation to elevations shown in the plan s or approved by the Engineer. Excavate holes at pile locations with diameters that will result in at least 3 inches of clearance all around piles. Before filling holes, support piles in their planned location within excavations and when noted in the plan s, drive piles to th e required driving resistance. Remove any fluid s from excavations and, at the Contractor’s option, fill holes with concrete , grout or flowable fill unless required otherwise in the contract.
1.Pile Excavation Use equipment with sufficient capacity to drill through soil, rock, boulders, timbers , man-made objects and any other materials encountered to a depth of at least 5 feet deeper than the maximum pile excavation length shown on the plans . Do not use blasting to advance pile excavations. Blasting for cor e removal is only permitted when approved by the Engineer. Contain and dispose of drilling spoils as directed and in accordance with Section 802. Drilling spoils consist of all materials and fluids removed from pile excavations. If unstable, caving or sl oughing soils are anticipated or encountered, use slurry or temporary steel casings to stabilize holes . When using slurry, submit slurry details including product information and additives , manufacturer’s recommendations for use, slurry equipment details and documentation that mixing water is suitable for slurry before beginning drilling. When using temporary casings, use smooth non- corrugated clean watertight steel casings of ample strength to withstand handling and installation stresses and pressures imposed by concrete, earth , backfill and fluids . Use steel casings with an outside diameter equal to the hole size and a wall thickness of at least 1/4 inch.
2.Filling Holes Check the water inflow rate at the bottom of holes after all pumps have been removed. If the water inflow rate is greater than 6 inches per half hour or holes are stabilized with slurry , place concrete, grout or flowable fill with a method that meets Subart icle 411-4(E)(2) except use a pump hose or tre mie with a diameter small enough to fit between the pile and side walls . Otherwise , remove any fluids and free fall concrete, grout or flowable fill into holes. Ensure that concrete, grout or flowable fill flows completely around piles. Place concrete, grout or flowable fill continuous ly and remove all temporary casings.
F.High -Strain Dynamic Pile Testing (Dynamic Pile Testing) When required, test piles in accordance with ASTM D4945 using dynamic pile testing equipment with external transducers manufactured by Pile Dynamics, Inc. or another approved vendor. Approved vendors can be found on the Geotechnical Engineering Unit’s website . Analyze collected data using signal matching software ( CAse Pile Wave Analysis Program (CAPWAP) manufactured by Pile Dynamics, Inc. or equivalent by another approved vendor). Use a prequalified consultant to perform dynamic pile testing and signal matc hing analys es and provide dynamic pile testing reports. U se a dynamic pile testing operator approved as a Field Engineer (key person) for the dynamic pile testing consultant . Provide dynamic pile testing reports signed and sealed by an engineer approved as a Project Engineer (key person) for the same dynamic pile testing consultant .
4-72 Test piles in accordance with the plans or as directed by the Engineer . Provide piles for
dynamic pile testing with lengths shown in the plan s. Do not drive piles until the proposed pile driving methods and equipment ha ve been preliminarily accepted. Notify the Engineer of the pile driving schedule at least 7 days in advance. The Engineer will complete the review of the proposed pile driving methods and equipment within 7 days of receiving dynamic pile testing report s and pile driving criteria . Do not place concrete for caps or footings on piles until dynamic pile testing reports and pile driving criteria have been accepted by the Engineer and the piles have been successfully driven to this criteria .
1.Dynamic Pile Testing If necessary, provide a shelter to protect the dynamic pile testing operator and equipment from conditions of sun, water, wind and temperature. The shelter should have a floor size of at least 6 feet x 6 feet and a roof height of at least 8 f eet. If necessary, heat or cool the shelter to maintain a temperature between 50°F and 85°F. Place the shelter within reach of the dynamic pile testing cables and clear view of piles being driven. Drill holes for dynamic pile testing transducers as directed by the Engineer . Place piles in leads and templates before attaching dynamic pile testing transducers . Use only preliminarily accepted pile driving methods and equipment to drive piles. Drive piles as directed by the Engineer and in accordance with Subarticle 450 -3(D). The dynamic pile testing operator or Engineer may require modif ied pile installation procedure s during driving, including but not limited to driving piles deeper or to a higher driving resistance than stated in the plans . Dynamic measurements will be recorded and used to evaluate the hammer performance, driving resistance and stresses, energy transfer, pile integrity and various soil parameters such as quake and damping. If required, reattach dynamic pile transducers and restrike or redrive pile s in accordance with Subarticle 450 -3(D)(4). Obtain the required stroke and at least 6 inches of pile movement as directed by the Engine er. Dynamic measurements will be recorded during restriking and redriving. The Engineer will determine when dynamic pile testing has been satisfactorily completed.
2.Signal Matching ( CAPWAP or equivalent) Analysis Non-automated, independent signal matching analysis is required for a t least a hammer blow near the end of initial drive and each restrike and redrive. Additional signal matching analys es may be required as determined by the dynamic pile testing consultant or Engineer.
3.Dynamic Pile Testing Report s Submit a copy of each dynamic pile testing report within 7 days of completing dynamic pile testing. The dynamic pile testing report format shall be in accordance with NCDOT dynamic pile testing format requirements . Include the following in dynamic pile testing reports:
a.Title Sheet
i.Department’s TIP number and WBS element number (ii) Project description (iii) County (iv) Bridge station number
v.Pile location (vi) Personnel (vii) Report date
4-73 (b) Introduction
c.Site and Subsurface Conditions (including water table elevation)
d.Pile Details (including driving dates and times)
i.Pile type and length (ii) Required driving resistance and resistance factor (iii) Concrete compressive strength or steel yield strength (iv) Pile splice type and locations
v.Pile batter (vi) Insta llation methods including use of predrilling, spudding, vibratory hammer, template, barge, etc.
e.Driving Details
i.Hammer make, model and type (ii) Hammer and pile cushion type and thickness (iii) Pile helmet weight (iv) Hammer efficiency and operation data including fuel se ttings, bounce chamber pressure, blows per minute, equipment volume and pressure
v.Driving data (ram stroke, blows /ft and set for last 10 hammer blows) (vi) Ground or mud line, template reference and final pile tip elevations (vii) Restrike and redrive information
f.Dyna mic Pile Testing Field Work Details
g.Signal Matching Analysis Results
i.Table showing percent skin and tip, skin and toe damping, skin and toe quake and match quality.
h.Pile Driving Criteria Analyze pile driving with the GRL Wave Equation Analysis Program (GRLWEAP) manufactured by Pile Dynamics, Inc. or another approved Wave Equation Analysis Program (WEAP) developed by the approved dynamic pile testing equipment vendor. Use the same dynamic pile testing consultant that provides dynamic pile testin g reports to perform GRLWEAP /WEAP analyses and develop pile driving criteria. Provide driving criteria sealed by an engineer approved as a Project Engineer (key person) for the same dynamic pile testing consultant. Analyze pile driving so driving stresses, energy transfer, ram stroke and blows per foot from dynamic pile testing and resistances from signal matching analyses correlate to GRLWEAP /WEAP models. Provide pile driving criteria for each combination of required driving resistance and pile length installed for all pile types and si zes. Submit a copy of pile driving criteria with dynamic pile testing reports. Include the following for driving criteria.
i.Table showing blows per foot and equivalent set vs. either stroke for multiple strokes in increments of 6 inches (ii) Maximum stroke or blows per foot or pile cushion requirements to prevent overstressing piles as needed (iii) GRLWEAP /WEAP software version information (iv) PDF copy of all pile driving criteria and executable GRLWEAP /WEAP input and output files
v.Attachments
4-74 A) Boring log(s)
B.Pile drivin g equipment data form (from Contractor)
C.Field pile driving inspection data (from Engineer)
D.Accelerometer and strain gauge serial numbers, calibration and locations
E.Dynamic pile testing hardware model and signal matching ( CAPWAP or equivalent) software vers ion information
F.PDF copy of all dynamic pile testing data and executable signal matching (CAPWAP or equivalent) input and output files
450-4 Measurement and Payment
No additional payment will be made for subsurface investigations to determine required pile lengths or larger caps or footing s due to piles out of position . Pile Driving Equipment Setup for ____ Prestressed Concrete Piles , Pile Driving Equipment Setup for ____ Steel Piles and Pile Driving Equipment Setup for ____ Galvanized Steel Piles will be measured and paid in units of each. Setting up equipment to drive piles will be measured as one per pile. No payment will be made for pile driving equipment setup f or installed piles that are not driven. The contract unit price for Pile Driving Equipment Setup for ____ Prestressed Concrete Piles, Pile Driving Equipment Setup for ____ Steel Piles and Pile Driving Equipment Setup for ____ Galvanized Steel Piles will b e full compensation for mobilizing and demobilizing pile driving equipment, personnel, supplies and incidentals, setting up and breaking down pile driving equipment, e.g., pile hammer, crane, template, etc. and submitting the proposed pile driving methods and equipment. ____ Prestressed Concrete Piles, ____ Steel Piles and ____ Galvanized Steel Piles will be measur ed and paid in linear feet . Steel piles will be measured as the pile length before installation minus any pile cut- offs. Prestressed concrete piles will be measured as the authorized pile length before installation. No payment will be made for pile cut-offs or cutting off piles. No payment will be made for damaged, defective or rejected piles or any piles for false work, bracing, templates or temporary work bridges. The contract unit prices for ____ Prestressed Concrete Piles, ____ Steel Piles and ____ Galvanized Steel Piles will be full compensation for furnishing and installing piles except for the items paid for separately in this article. Composite piles will be measured as the pile length of the prestressed concrete and steel H-pile sections before installation minus any pile cut- offs. The concrete and steel sections will be measured and paid at the contract unit p rices for ____ Prestressed Concrete Piles and ____ Steel Piles , respectively. No payment will be made for portions of steel H -pile sections embedded in prestressed concrete sections or steel pile splicers and any associated hardware or welding. After steel piles attain the required resistance and pile penetration and at the Contractor’s option, drive piles to grade in stead of cutting off steel piles provided the remaining portions of steel piles do not exceed 5 feet and steel piles can be driven without damage or exceeding the maximum stroke or refusal. When this occurs, the additional pile length driven will be measured and paid at the contract unit prices for ____ Steel Piles and ____ Galvanized Steel Piles . For prestressed concrete piles that are built up, the build -up will be measured and paid at the contract unit price for ____ Prestressed Concrete Piles. Steel pile tips are not included in the measurement of prestressed concrete piles. No separate payment will be made f or steel pile tips or splicers and any associated hardware or welding. Steel pile tips and steel pile splicers will be incidental to the contract unit price for ____ Prestressed Concrete Piles . Steel Pile Points and Pipe Pile Plates will be measured and p aid in units of each. Steel Pile Points and Pipe Pile Plates will be measured as one per pile. Predrilling for Piles will be measured and paid in linear feet . For bents with a predrilling pay item shown in the plans, predrilling will be paid as Predrilling for Piles and measured per pile
4-75 location as the depth from the ground or mud line to the specified predrilling elevation or
revised elevation approved by the Engineer. The contract unit price for Predrilling for Piles will also be full compensation for using temporary casings. For bents without a predrilling pay item shown in the plan s, predrilling will be incidental to the contract unit prices for ____ Prestressed Concrete Piles, ____ Steel Piles and ____ Galvanized Steel Piles. No direct payment will be made for spudding. Spudding will be incidental to the contract unit prices for ____ Prestressed Concrete Piles, ____ Steel Piles and ____ Galvanized Steel Piles. Pile Redrives will be measured and paid in units of each. Pile Red rives will be measured as the number of restrikes or redrives required by the Engineer. No payment will be made for restrikes or redrives when the Contractor chooses to restrike or redrive piles. Pile Excavation in Soil and Pile Excavation Not in Soil will be measur ed and paid in linear feet . Pile excavation will be measured as the depth from the ground line to the specified pile excavation elevation or revised elevation approved by the Engineer. Define “n ot in soil ” as material with a rock auger penetra tion rate of less than 2 inches per 5 minutes of drilling at full crowd force. When not in soil is encountered, seams, voids and wea thered rock less than 3 feet thick with a rock auger penetration rate of greater than 2 inches per 5 minutes of drilling at full crowd force will be paid at the contract unit price for Pile Excavation Not in Soil. Seams, voids and weathered rock greater than 3 feet thick will be paid at the contract unit price for Pile Excavation in Soil where not in soil is no longer encount ered. The contract unit prices for Pile Excavation in Soil and Pile Excavation Not in Soil will be full compensation for stabilizing and filling holes with concrete , grout or flowable fill. Dynamic Pile Testing will be measured and paid in units of each. Dynamic Pile Testing will be measured as one per pile. The contract unit price for Dynamic Pile Testing will be full compensation for performing dynamic pile testing the first time a pile is tested, performing non- automated signal matching (CAPWAP or equivalent) analys is on data collected during initial drive, restrikes and redrives , providing dynamic pile testing report s, performing GRLWEAP /WEAP analysis and developing and providing pile driving criteria . Subsequent dynamic pile testing of the same piles will be incidental to the contract unit price for Pile Redrives . The contract unit price for Dynamic Pile Testing will also be full compensation for the Contractor’s assistance to perform dynamic pile testing during initial drive, restrikes and redrives. Payment will be made under : 450 Pay Item Pay Unit Pile Driving Equipment Setup for ___ Prestressed Concrete Piles Each Pile Driving Equipment Setup for ___ Steel Piles Each Pile Driving Equipment Setup for ___ Galvanized Steel Piles Each ____ Prestressed Concrete Piles Linear Foot ____ Steel Piles Linear Foot ____ Galvanized Steel Piles Linear Foot Steel Pile Points Each Pipe Pile Plates Each Predrilling for Piles Linear Foot Pile Redrives Each Pile Excavation in Soil Linear Foot Pile Excavation Not in Soil Linear Foot Dynamic Pile Testing Each
Source: North Carolina Standard Specifications for Roads and Structures, 2024 Edition. Pages 203–211 of 857.