Gantries 16-1

CHAPTER 16 - GANTRIES

DS Temple

16.1 SCOPE

This section covers the inspection of Sign Gantries as specified in the applicable chapter of the

Specifications. It also covers the special attention which must be given by the engineer’s monitoring

staff to the specific requirements of setting out, excavations foundations, backfill and, manufacture

and erection of the structural steel gantries.

16.2 FOUNDATIONS

16.2.1 Setting Out (Refer to Chapter 4)

The setting out of the gantries should be carried out in accordance with Chapter 3 of this document.

However the following points should be noted.

16.2.1.1 Location

The gantry location (e.g. km distance) on the structural drawings must tie in with the location given

on the road works drawings.

16.2.1.2 Horizontal Clearances

Horizontal clearances must be checked prior to the casting of the gantry foundation plinths.

16.2.1.3 Vertical Clearances

The vertical clearances as specified on the design drawings should be checked by the Monitoring Staff

on site.

Photo 16.1: Gantry foundation

16.2.2 Excavations (Refer to Chapter 4)

Note that it is preferred that the foundation concrete is cast directly against the sides of the excavation.

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16.2.3 Formwork & Falsework (Refer to Chapter 6)

16.2.4 Steel Reinforcement (Refer to Chapter 7)

16.2.5 Concrete (Refer to Chapter 8).

Note that durability concrete should be used only in extreme situations.

16.2.6 Built-in Items

• The Monitoring Staff should confirm the orientation of the Holding Down Bolt Groups.

• Confirm the position of ducts, gantry number and any other built-in items indicated on the

drawings.

Photo 16.2: Completed gantry foundation

16.3 STRUCTURAL STEEL GANTRIES

16.3.1 Materials

The Engineer’s Monitoring Staff should ensure that the contractor submits a certificate of compliance

for:

• Structural steel for manufacture of gantry

• Holding down bolts

16.3.2 Corrosion Protection

The corrosion system as specified on the drawings must be confirmed with the Contractor. The

Monitoring Staff should ensure that the manufacturer’s Quality Assurance records are made available with the delivery of the gantries. Hot dip galvanizing could be specified as a corrosion protection

measure but should be used with caution as this process is still in the experimental stages. Buckling

of thin plates occurs during the dipping process due to stress relief in the plates and therefore extreme

care should be taken before using this method of corrosion protection.

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16.3.3 Shop Drawings

The Monitoring Staff should ensure that shop drawings of the gantry and holding down bolts are

submitted for review timeously.

16.3.4 Factory Inspection

It is a requirement that monitoring staff inspect the structural steel during the manufacturing process.

The following important aspects should be checked and verified against the design drawings:

• Dimensions and thicknesses of the steel plates.

• Number and spacing of the beam and column stiffener plates.

• Type, size and quality of all the welds as specified on the drawings.

• Diameter and length of anchor bolts, as well as the dimensions of the anchor bolt cage.

The Monitoring Staff should ensure that the correct grade steel for the anchor bolts and structural steel

gantry structure is used. All certificates pertaining to the grade and quality of the steel should be

obtained from the manufacturer for construction record purposes.

Photo 16.3: Gantry manufacturing

16.3.5 Erection

• The Monitoring Staff should ensure that the Contractor submits for review a complete method

statement for the erection of the gantries.

• Accommodation of traffic measures should be submitted in accordance with Road Traffic Signs

Manual, Chapter 13.

• Monitoring Staff should ensure that the gantry is erected within the specified tolerances.

16.4 CHECKING AND TESTING

The Monitoring Staff should visit the manufacturing facility during manufacture to ensure that the

gantries are being manufactured according to the Manufacturer’s Quality Plan.

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16.4.1 Corrosion Protection

• Reference should be made to the notes on the Detailed Design drawings for the corrosion

system to be used.

• Surface preparation to SA 2.5 should be checked prior to the application of any corrosion

protection.

• Ensure that the contractor’s proposed system for the painted, galvanized or sprayed metal

coating conforms to specified requirements.

• Random testing of the thickness of the various coats of the corrosion protection system should

be carried out in the paintshop as well as on the delivered elements and especially on the site

painted areas (welded site connections on gantry beams).

• Records of the tests carried out on the dry film thicknesses (DFT) should be kept.

16.4.2 Welding

The Monitoring Staff should ensure that the process control adopted by the manufacturer complies with the Project Specification. This can be achieved by including notes on the shop drawings for

welding procedures. All QA records of process control of the welds should be provided to the

Engineer.

Proof of the welder’s qualifications should be provided.

Ultrasonic testing should be carried out on the following welded connections:

Column & base plate connection

Column & beam haunch connection At least 10% of the seam welds in the columns*

At least 10% of the seam welds in the beams*

Gusset plate connections*

Site welds**

*Where ultrasonic testing is not possible magnetic particle testing should be carried out on at least

50% of the seam welds.

**At the very least site welds should be inspected and approved by an independent qualified person. Where possible ultrasonic testing (preferable) or magnetic particle testing should be carried out. It

should be noted that these must be done before painting and after the steel has cooled.

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Photo 16.4: Gantry erection

16.5 GANTRY STRUCTURES - CONSTRUCTION MONITORING CHECK LIST

The Monitoring Staff should use the “Gantry Structures - Construction Monitoring Check List” as far

as possible to ensure the quality of the gantry structures.

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INDEX TO APPENDICES

16A - GANTRY STRUCTURES

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CONSTRUCTION MONITORING CHECKLIST

PROJECT NO. / NAME: .......................................................................................................................................

INSPECTOR’S NAME(S): ....................................................................................................................................

STRUCTURE: ........................................................... ELEMENT: ..............................................................

ACTIVITY AND DETAILS APPROVAL

SIGNED DATE Y/N N/A Comment

1. EARTHWORKS

1.1 Setting out

• Km distance

• Depth of excavation relative to edge of

road

• Distance from edge of road to

foundation centre

• Can foundation be cast directly against

side of excavation as is preferred

• If not has work space been agreed

with Engineer

1.2 Bearing pressure

• DCP Tests done

• Is soil improvement required

• If so describe

• Soil improvements tested

• Provide estimated foundation bearing

capacity in kPa

1.3 Blinding layer

• Depth to blinding layer relative to

edge of road

• Plan area of blinding layer

2. REINFORCEMENT

2.1 Footing – Bars parallel to road

• Are they Top 1 and Bottom 1

• Bar spacings - 125mm

• Bar type bottom

• Bar type top

• Alternative bar reversed (top bars)

2.2 Footing – Bars perpendicular to road

• Bar spacings - 250mm

• Bar type bottom

• Bar type top

• Alternative bar reversed (top bars)

2.3 Plinth

• Are there the correct number of "U"

bars

• Orientation

• Location

• Bar projection height

• Secondary bars, i.e. clips & stirrups

Checklist continues on next page…

GANTRY STRUCTURES

CHECK LIST(1/4)

APPENDIX 16A

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ACTIVITY AND DETAILS APPROVAL

SIGNED DATE Y/N N/A Comment

3. ANCHOR BOLTS

3.1 In workshop

• Diameter

• Steel Grade of bolt

• Bolt cage dimensions

3.2 On Site

• On site orientation

• Location within plinth

• Projection of bolts

• Top portion of bolt corrosion

protected

4. FORMWORK

4.1 Footing plan dimensions

4.2 Is footing formwork required and

approved

4.3 Footing thickness

4.4 Plinth plan dimensions (parallel and

perpendicular to road)

4.5 Height of plinth

4.6 Level difference between top of

plinth & road edge

4.7 Cover to rebar - footing 50mm

bottom, 75mm sides

4.8 Cover to rebar - plinth 50mm sides

and top

4.9 Plinth shutter - adequately propped

4.10 Plinth off shutter surface finish OK

5. SPECIAL CAST IN ITEMS

5.1 PVC ducts provided if detailed on the drawings

5.2 Location in plinth (plan)

5.3 Projection above plinth concrete

Checklist continues on next page…

GANTRY STRUCTURES

CHECK LIST(2/4)

APPENDIX 16A

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ACTIVITY AND DETAILS APPROVAL

SIGNED DATE Y/N N/A Comment

6. CONCRETE

6.1 Pre concrete inspections

• Concrete as per specification & mix

design (obtain copy of delivery note)

• Concrete Class W30MPa

• Plinth concrete: 50mm < slump <

70mm

• Proposed curing method

• Proposed curing period

6.2 Post concrete inspections

• Cracks

• Spalling

• Honeycomb

• Shutter kick

• Repair method

7. STRUCTURAL STEEL

7.1 Prior to dispatch to site

• Steel grade certificate and markings

• Column height plust the beam section

• Beam length (less the beam section

attached to column/s)

• Column cross section dimensions

• Beam cross section dimensions

• Plate thicknesses columns

• Plate thicknesses beams

• Special attachment size & plates

• Stiffener plates, thickness, spacing,

fitment

• Welds visually acceptable and

according to drawing

• Chamfering and preparation for

welding

• Holes setting out

• Ultrasonic testing of welds - certified

7.2 On site

• Method of erection approved

• Traffic accommodation approved

• Site welding method approved

• Site welding quality approved

• Anchor bolt tightening torque (provide

Nm)

• Grout under base plate - type approved

• Grout under base plate - installed

correctly

Checklist continues on next page…

GANTRY STRUCTURES

CHECK LIST(3/4)

APPENDIX 16A

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ACTIVITY AND DETAILS APPROVAL

SIGNED DATE Y/N N/A Comment

8. CORROSION PROTECTION

• Inland or coastal specification

• Paint specification approved

8.1 Prior to dispatch to site

• Abrasive blast cleaning

• Primer - paint type and DFT certified

• Approval of application of second coat

prior to dispatch

8.2 On site

• Patch repairs- paint type and DFT

certified (NB repairs at site welds)

• Second coat - paint type and DFT

certified

• Final coat - paint type and DFT

certified

• Final coat colour

• Anchor bolts corrosion protected

9. AS-BUILT DATA

• Name and address of Main Contractor

• Name and address of Steelwork

Fabricator

• Name and address of Painting

Contractor

• Paint system used

• Foundation material and safe bearing

capacity

• Date of steel structure erection

Least favourable results of test certificates:

9.1 Structural steel

• Steel grades

• Ultimate tensile strength (MPa)

• Yield strength (MPa)

• Elongation at fracture (%)

9.2 Anchor bolts

• Steel grades

• Ultimate tensile strength (MPa)

• Yield strength (MPa)

• Elongation at fracture (%)

9.3 Data included an “As-built”

drawings

GANTRY STRUCTURES

CHECK LIST(4/4)

APPENDIX 16A