Bridge Design for Construction Safety · 2020. 10. 31. · 2020 Virtual Short Course October 13,...

2020 Virtual Short Course October 13, 2020

Bridge Design for Construction Safety

Robert D. Owens, P.E.

October 13, 2020

PresenterPresentation NotesI am going to cover a little background on the reason why Designing with Construction Safety in mind is important. Then I will get into some specific items we can consider.


Table of contents

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Overview

Importance of designing for construction safety

How to design for construction safety

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2

3


Overview

Construction is one of the most hazardous occupations. This industry accounts for

• 8% of the U.S. workforce, but 20% of fatalities

• About 1,000 deaths annually

• About 170,000 serious injuries annually

[CPWR 2019]

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PresenterPresentation NotesAs many of us know, construction is one of the most dangerous industries for workers. In the United States, construction typically accounts for 170,000 serious injuries and 1,000 deaths each year. The fatality rate is disproportionally high for the size of the construction workforce. 1 in 5 workplace fatalities occurs in construction.

CPWR [2019]. Center for Construction Research and Training. Photo courtesy of CPWR


Overview

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PresenterPresentation NotesTypically, when we think of construction safety we think of PPE. But that is actually the last resort. Design flaws are frequently contributed to accidents. Twenty percent of all collapses during construction are the result of structural design errors.


Overview

5

ELIMINATIONBEST BESTDesign it out

SUBSTITUTIONUse something else

ENGINEERING CONTROLSIsolation and guarding

ADMINISTRATIVE CONTROLSTraining and work scheduling

PERSONAL PROTECTIVE EQUIPMENTLast resort

Controleffectiveness

Businessvalue

Hierarchy of Controls per ANSI/AIHA Z10-2005

PresenterPresentation NotesPersonal Protective Equipment (PPE): Includes but is not limited to safety glasses for eye protection; ear plugs for hearing protection; clothing such as safety shoes, gloves, and overalls; face shields for welders; fall harnesses; and respirators to prevent inhalation of hazardous substances. Administrative controls: Job rotation, work scheduling, training, well-designed work methods, and organization are examples. Administrative controls include training modules and company procedures. A well-organized worksite is safer than a messy one. Reducing the clutter on a construction site improves worker safety by reducing the exposure to hazards. The foreman controls site layout and housekeeping policies. Engineering controls: Isolate process or equipment or contain the hazard. Remove hazard from work zone, e.g., with exhaust ventilation. Require two hands to operate machinery. Use warning devices to warn worker about entry into hazard zone. Signs, labels, alarms, and flashing lights give warnings. Safety switches, hand guards, and other engineering controls prevent certain kinds of injuries. Substitution: Substitute less-hazardous materials, processes, operations, or equipment. A larger crane may be specified when the load or the reach approaches the crane design limit. Nontoxic chemicals are preferred. The Green Chemistry movement replaces toxic compounds with less hazardous chemicals. Elimination: “Design out” hazards and hazardous exposures.

2020 Virtual Short Course October 13, 2020 6

Why Design for Construction Safety?


TEXAS ENGINEERING PRACTICE ACT AND RULES CONCERNING THE PRACTICE OF ENGINEERING AND PROFESSIONAL ENGINEERING LICENSURE

§137.55 Engineers Shall Protect the Public(a) Engineers shall be entrusted to protect the health, safety, property, and welfare of the public in the practice of their profession. The public as used in this section and other rules is defined as any individual(s), client(s), business or public entities, or any member of the general population whose normal course of life might reasonably include an interaction of any sort with the engineering work of the license holder.

Importance of Ethics

PresenterPresentation NotesThere are many reasons why considering designing for safety is a good idea. But the only one I am going to talk about today is the ethics.


Design for Construction Safety

How to Design for Construction Safety



Identify the hazards

– Utilities

– Excavations

– Falls and falling objects

– Structural Collapse

– Traffic

PresenterPresentation NotesIn order to design out hazards, you must identify what the hazards are for each phase and type of construction.



Design to mitigate the hazards, if possible– Demolition

– Foundations

– Columns

– Bent Caps

– Beam Erection• Concrete• Steel

– Slab

– Phased Construction

– Traffic

PresenterPresentation NotesI am going to talk about some of the ways to design these out in the following slides by taking us thru the construction of a bridge.



Demolition

PresenterPresentation NotesThe first task with most projects to ask is, whether demolition will be taking place.



Item 496 Construction

– Demolition plans should include the type and location of equipment to be used, the method and sequence of removal and a narrative indicating the stability of the partially demolished structure throughout the demolition process.

PresenterPresentation NotesDemo plans are provided by the contractor, but it is still our responsibility to review.



When is a P.E. required to sign and seal a set of demolition plans? – Does demo plan affect public

safety? – Will traffic pass under bridge?– Does traffic return to bridge after

partial demo?

PresenterPresentation NotesThere are requirements for demo plans, these are the questions to ask when demo plans have to be signed and sealed by an engineer.



Consider providing demolition plan in the contract plans: – Variable depth CIP girders – Other bridge types where partial

span demolition can create unstable structure

– Consider construction loads at critical stages of construction

– Provide at least 1 option for removal

PresenterPresentation NotesIf there are complex stages required for demo, consider providing demo plans, at least one option. Consider the loads, temp, for each phase of the demo.



Foundations

PresenterPresentation NotesThe first task is to install the foundations, whether it be driving piles or drilled shafts.



Hazards during Foundation construction– Utilities

– Excavations

PresenterPresentation NotesThe first task is to install the foundations, whether it be driving piles or drilled shafts.



Utilities

– Clearance of Underground Utilities

• Try to have one diameter clear distance between the edge of the pipe and the edge of the foundation element.

• Increase this distance if uncertainty exists.

– Location of Aboveground Utilities

PresenterPresentation NotesOne of the first hazards you need to consider is the utilities. When placing your bent or abutment lines and then the individual piles or shafts, you need to consider the clear distance between the edge of the pipe and the edge of the foundation element. Take into consideration that the utility may not be exactly where you think it is and that the foundation element may be not in the exact location you called for due to construction tolerances. Also, take into account the size of the pipe conveying the water, wastewater, or gas. It may be a single, thin line on the plan sheet, but it could be 6-inches to 6-feet in diameter. All of these things need to be considered when determining where to place your foundation elements.

While thinking about the underground utilities, don’t neglect the above ground ones. Overhead power lines complicate the installation of most everything. Consider having these relocated prior to construction beginning or placing elements significantly away from overhead lines.

For both underground and above ground, clearly show them on your plan sheets as well as the size of the pipe for below ground.



Excavations

– Temporary Special Shoring will likely be needed

• To replace a bridge with a longer bridge

PresenterPresentation NotesThe second hazard you need to consider when placing foundations is excavations. The responsibility of keeping excavations open and stable belongs to the Contractor, but the one things we can do is notify them on the need and provide the bid tab for temporary special shoring. You will likely need TSS when replacing a bridge with a longer bridge.



PresenterPresentation NotesThe new bridge is actually the same length as the old, but the structure was offset to left by 5 feet to avoid the old foundations. We had to maintain one lane of traffic during construction, so the existing roadway had to be shored, while the 1st phase was being constructed. Excavation greater than 5 feet require shoring.



Excavations

– Temporary Special Shoring will likely be needed

• For footing installation

PresenterPresentation NotesIf the contractor does not have the space to lay back the slope, which is common in urban areas, then the footing construction will require shoring. Shoring is required for 5 feet or deeper per OSHA. Footings typically require 1 to 2 feet of cover and are 4 to 5 feet deep. This means at least a 5-foot excavation. This excavation will need to be laid back or shored.



Columns



Columns

– Falls and Falling Hazards


– Traffic

PresenterPresentation NotesDuring traditional column construction, the main hazards are the failure of the formwork, falls, and falling objects.

The stability of the formwork is the contractor’s responsibility, but one way we can help, is to provide sufficient room for bracing of the formwork and a protected work zone around the column. How much is enough room? As much as you can give them. There is not an exact answer, but try to work with your traffic control designers to optimize space.



Precast Columns

PresenterPresentation NotesAnother solution is to use precast columns. In high traffic areas or areas where you cannot provide a comfortable work zone, consider using precast columns. These will limit the amount of time the workers are exposed to dangerous conditions. In the above pictures, the precast portion was used as a permanent form. The hollow columns where lowered around a cage of reinforcement and then the center was filled with concrete.



Segmental Columns

PresenterPresentation NotesSegmental columns are also an option.



Bent Caps

PresenterPresentation NotesOnce the columns are in place, the bent cap is constructed.



Bent Caps

– Falls and Falling Hazards


– Traffic

PresenterPresentation NotesAll of this work occurs in the air, so falls and falling objects are the hazards.



Bent Caps

– Consider Precast

• For standard bridges, just include the standards. – PBC-RC for round columns– PBC-P for piles

• For larger or non-standard precast bents, – Consider the weight– Design for erection

PresenterPresentation NotesOver 75 tons, the lifting and hauling of the piece gets complicated. Design your precast bent considering construction, note on the plans the lift points you design for, but allow for alternate designs. Try to limit the weight to less than 200 tons. Larger loads require larger cranes, which have to fit somewhere.



PresenterPresentation NotesPrecast bent caps on round column



PresenterPresentation NotesPrecast bent and abutment cap on concrete piles



Pre-Tensioned Precast Cap

– Current standard• PPBC-RC

– Replaces conventional flexure reinforcing with 0.6” prestressing strands

– Multiple shear reinforcing options• Welded wire reinforcing • Conventional stirrups• Square spirals

PresenterPresentation NotesPrestressed, Precast Bent Cap Option for Round Columns



Inverted-T Straddle

Rectangular Straddle

PresenterPresentation NotesNext we will discuss the special considerations for the safe construction of straddle caps.



PresenterPresentation NotesFrequently, straddle bents will require temporary shoring to support the form work during construction. Temporary shoring needs to be protected from traffic. Coordinate with your traffic control designer. This location is not above traffic, therefore shoring can be placed directly below the cap during construction.



PresenterPresentation Notes

Shore towers may not be able to go in ideal places or traffic may need to be maintained thru the bent during construction, so you may need pass thru forms, which can end up pretty deep. When crossing a road that has to stay open during construction, consider the vertical clearance with respect to the depth of the forms needed.



PresenterPresentation NotesAlternately, consider precast straddle caps. But don’t forget to take into consideration the weight of the precast element. The cranes needed to erect the piece need space to work in.



Concrete Beam Erection

PresenterPresentation NotesAlternately, consider precast straddle caps. But don’t forget to take into consideration the weight of the precast element. The cranes needed to erect the piece need space to work in.



Beam Erection - Concrete

– Falls and Falling Objects


– Traffic




Tx Girders

PresenterPresentation NotesThe Tx-Girders are more stable than the old I-Beams shapes and have a wide top flange, both of these make the beams safer during erection and subsequent deck construction.



PresenterPresentation NotesThese must be braced until the slab is cast and cured. This photo is showing the old style of bracing.



Minimum Bracing and Erection Standards

– MEBR-C, Released August 2017

– For I-Girders

– Cross-bracing, which was shown to be ineffective at stabilizing girders, is eliminated and horizontal bracing is now used at all locations.

– A new option for top bracing, a steel strap placed beneath the prestressed concrete panels, is provided. This option eliminates the need to remove and reattach bracing during panel placement.

– The bracing spacing is simplified, to aide installation and inspection of the bracing.


These new standards are a safer way of bracing than the old, because of eliminating the need to remove bracing.



Steel Beam Erection




Beam Erection - Steel



– Traffic

PresenterPresentation NotesSomeone has to put together this jigsaw puzzle called a steel bridge in the air while either sitting on the placed beams or sitting in a cherry picker. And it take many people. Notice the guy sitting on a platform between the two bottom flanges. Two guys in buckets, and one on the top of the beam.

Wider beams make safer walking platforms.


Design for Construction Safety Prefabrication

– Shop work • Safer• Minimize the number of field splices

– Keep in mind the weight and size of sections

Connections– Allow a bolted option– Avoid awkward or dangerous connection locations.– Avoid sharp corners– Keep the connection simple.

Cross-Frame Half Pipe Stiffeners– Skewed Bridges

Lean-On Bracing– Straight Bridges

PresenterPresentation NotesShop Work – Faster, Less expensive, More consistent, Better quality

Consider the use of the half pipe stiffeners for connection details on highly skewed bridges (research project 5701). They are expected to be an easier fit-up, thereby minimizing the amount of time required in the air.

Consider Lean-on Bracing to reduce the number of braces on the bridge. Fewer braces mean less time in the air.



Steel Girder Erection/Construction One Main Concern of OwnerSAFETY

• Has a PE designed a plan that will not put public safety at risk?• Has lateral loading been considered?• Are traffic control issues clearly defined?• Site conditions have an influence on the thoroughness of our review.• Is the plan being followed?

PresenterPresentation NotesI am only going to talk about the changes that relates to the topic of this presentation.



Interchange Construction

– Traffic Control

– Shoring Towers

– Staging of cranes

– Typically require weekend closures

PresenterPresentation NotesWith the need to keep traffic moving, more and more, we are seeing even less than weekend closures for beam erection. Balance the need for traffic and the safety of the worker. Remember, they may need to erect a shore tower, hang beams, and take the show tower down. That is a lot of work, give the contractor the time to do it safely. Consider, staged closures. Can you close to one-lane, put in concrete barriers, erect the shore tower, then do a full closure, erect the beams, open one lane back up, remove the shore tower, then open fully to traffic? What I am trying to get here is think outside the box? Are weekends really the worst traffic time, then allow for weekday closures?

Work with the traffic control designer to come up with a plan that provides the space for shore towers, multiple cranes, and traffic.



PresenterPresentation NotesNote the barrier on roadway surface for traffic control, and the overhang over roadway.



PresenterPresentation NotesNote the shore tower spanning the access road.



Slab

PresenterPresentation NotesNote the shore tower spanning the access road.



Slab


PresenterPresentation NotesHazards associated with slab construction.



Precast Concrete Panels

– Safety (immediate work platform)

– Quicker

– Panels seal better than PMDF

– No PMDF-Beam welds to break loose

– See the PCP and PCP(FAB) standards for more information

PresenterPresentation NotesHazards associated with slab construction.



Panels can be used

– For clear distance between beam flanges of 2’-10” to 10’-0”.

– For straight or skewed concrete beams

– For straight steel beams.

PresenterPresentation NotesPCP’s provide a safe working platform for the workers. Try to design to avoid having to have open holes where PMDFs or more conventional forming would be needed.



Traditional Construction at the end of a span/unit




Slab Overhangs

PresenterPresentation NotesWith PCP’s being used the most dangerous part of the deck installation is the slab overhangs. The erection of the overhang brackets create a fall and falling hazard.



Precast Overhangs

– Current developed standards– PCP(O) and PCP(O) FAB

ImprovedWork Area

PresenterPresentation NotesTradition overhang C-49 bracket, limited working room, tripping hazards, constrained work area.



Alternatives to Precast Panels

– Full Depth Prefab Deck and Girder Assemblies

• Challenges – Panel-to-Panel Joints (UHPC Closure)– Grinding of sacrificial depth to obtain

riding surface




Other precast beam options

– Adjacently Spaced Precast, Prestressed Beams (Box, Slab, and Decked Slab)

• Beams Placed Side-by-Side

• With Composite Slab

– Simpler Stay-in-place Formwork vs Typical Bridges

– Shear Keys

• With ACP Overlay Only

– Post-Tensioning or Welded Connections

– Durability Considerations




Phased Construction




Consider traffic needs and the placement of any temporary barriers.




Consider how much space is needed for traffic.


Try to have at least 11-foot lanes. For higher speeds, 12-foot would be better.



Consider how much space is needed between the two phases.


Try to have at least 11-foot lanes. For higher speeds, 12-foot would be better.



How do I get more space for the phase?– First ask can a detour be used?

– Consider reducing traffic to one-lane.

– Consider offsetting the alignment.

– Consider building a slightly wider bridge than is needed for the final condition.

– WORK with the TRAFFIC CONTROL PLAN designer.

PresenterPresentation NotesNote the worker sandwiched between the forms and the rail. He is standing on the 2 feet of slab left behind the rail.



PresenterPresentation NotesNote how close the forms and screen rail are to traffic. They appear to be directly behind the rail. This is a minimum amount of clearance. In order to just fit a screed in, the contractor needs 3 to 4 feet between phases.



PresenterPresentation NotesNote the worker sandwiched between the forms and the rail. He is standing on the 2 feet of slab left behind the rail.



Drainage




Don’t forget drainage during construction.

“Temporary” conditions can last several months to a year.

Likely to occur with constant cross-slope, phased construction.

PresenterPresentation NotesWhen you have a constant slope and phase replace it starting with demolishing the lower end first, if you use a solid barrier along the phase line, you can create ponding issues. Consider using an open barrier or a slotted CSB.



Traffic




Probably the biggest hazard on a construction site

Try to design so that the construction occurs behind a positive barrier at all phases.

WORK with your Traffic Engineers to come up with a plan that keeps the workers safe and still moves traffic.

ASK yourself would I feel safe doing this work?

PresenterPresentation NotesWorker's safety must be a priority.



Fully Prefabricated Spans




One of Safest Methods Significant Cost

Fully Constructed on Simulated Bearings

Transported to Final Location via SPMT’s, Slide-in or Other Means

Erected in a Few Hours

Significant Equipment Mobilization and Site Preparation

PresenterPresentation NotesWorker's safety must be a priority.



Contact for Questions:

[email protected]


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