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AIA CreditsElco Construction Products an Infastech company, is a Registered Providerwith The American Institute of Architects Continuing Education Systems. Creditearned on completion of this program will be reported to CES Records for AIAmembers. Certificates of Completion for non-AIA members available onrequest.This program is registered with the AIA/CES for continuing professionaleducation. As such, it does not include content that may be deemed orconstrued to be an approval or endorsement by the AIA of any material ofconstruction or any method or manner of handling, using, distributing, ordealing in any material or product. Questions related to specific materials,methods, and services will be addressed at the conclusion of this presentation.
Learning Objectives1. Identify situations requiring A/E to specify fasteners instead of leaving product selection to contractor or supplier.2. Learn techniques for reducing fastener damage due to rust and galvanic corrosion.3. Be able to explain causes of hydrogen embrittlement and HASCC.4. Be able to specify high performance fasteners that are HASCC resistant.5. Explain the role of fasteners in building sustainability.
For want of a fastener…“For want of a nail, the shoe was lost, For want of a shoe, the horse was lost, For want of a horse, the rider was lost. For want of a rider the battle was lost. For want of a battle the kingdom was lost. All for the want of a nail.”
For want of a fastener…This old rhyme about a battlebeing lost due to one missingnail is a parable about makingsure of the details.
For want of a fastener…Yet it’s specifically aboutfasteners, because they area particular kind of detail:a small thing that holdstogether larger and moreseemingly important things.
For want of a fastener…Compared to the horse andeven the shoe, the fastener issmall. Yet without it…
For want of a fastener…“God is in the details.” Mies van der Rohe
Your reputation hangs onspecifying the right fasteners. Fastener specification is critical to project success. The Petronas Towers in Kuala Lumpur, the world’s tallest building, required careful engineering to ensure none of the millions of fasteners used to install cladding would be the installation’s weakest link.
Your reputation hangs onspecifying the right fasteners. Standard types and grades of fasteners are sufficient in many construction applications. In these instances, fastener selection can usually be based on industry standards, building code requirements, and design loads.
Your reputation hangs onspecifying the right fasteners. It may be acceptable in some cases to leave fastener selection to contractors or building product fabricators, allowing them to select fasteners based on cost, convenience, and trade practice.
Your reputation hangs onspecifying the right fasteners. Other times, fastener selection can be one of the most crucial aspects of building design. Professional judgment is required to specify fasteners that: • Perform as intended • Are dependable & economical • Last the life of the building
A big job for such a small partFactors affecting fastener performanceinclude:• Structural capacity and safety factor. – Static and dynamic load resistance. – Pull-out and pull-over resistance. – Shear resistance of fastener and attached materials.
A big job for such a small partFactors affecting fastener performanceinclude:•Corrosion resistance in conditions of use.•Seal against liquid or gas leakage (if required).•Constructability, practicality, and inspectability.•Compatibility with design intent and aesthetics.•Removability, or other special requirements.•Service life exceeds that of attached materials.
A big job for such a small partSpecifying fasteners is part of designingsafe, durable, and practical connections between building components.
HASCCA “New” Threat to FastenersHASCC = Hydrogen-Assisted StressCorrosion Cracking.
HASCC A “New” Threat to FastenersHASCC has only been identified as afastener failure mechanism within the pastfew decades.
HASCC A “New” Threat to FastenersSince then, “Best Industry Practices” havechanged to protect fasteners againstHASCC.
Must it Rust?Most architectural fastenersare made from grades oralloys of steel that will reactwith oxygen to create ferrousoxide, commonly know asrust. Rust is a type ofcorrosion that weakens anddeteriorates steel.
Must it Rust?Rusting is accelerated whensteel is also exposed tomoisture, especially if themoisture contains chlorides(salts), a condition that iscommon in marine, industrial,and urban atmospheres.Once rust starts, it can spreadrapidly to adjacent exposedsteel surfaces.
Must it Rust?When designing steel-to-steelconnections, both thefasteners and the items beingjoined must be protectedagainst rusting.Steel building panels, forexample, can be protected byusing zinc galvanizing and ahigh-performance coating.
Must it Rust?As a general guideline,fasteners should havegreater corrosion resistancethan items being joined sothat fasteners do not becomeweakest link in connection.
Corrosion-Resistant Plating Fasteners are often protected with metallic plating. For example, zinc plating helps protect steel against exposure to air and moisture and provide a sacrificial, galvanic protection to steel.
Corrosion-Resistant Plating Hot-dipped galvanizing is widely used for large fasteners such as anchor bolts. The thick layer of zinc deposited in this process clogs the threads of smaller screws. On the other hand, thin coatings of electro-plated zinc applied to some screws do not provide sufficient corrosion resistance for exterior or high performance fasteners.
Corrosion-Resistant Plating Other types of metal plating, such as cadmium and chromates, provide greater corrosion-resistance than zinc. These materials are decreasing in usage, however, due to environmental concerns about heavy metals toxicity.
Corrosion-Resistant Plating Plating is no longer considered acceptable protection for high performance fasteners. In fact, it is counter-indicated for case-hardened fasteners, as will be discussed later in course.
Corrosion-Resistant Plating Fasteners are often protected with metallic plating. For example, zinc plating helps protect steel against exposure to air and moisture and provide a sacrificial, galvanic protection to steel.
Corrosion-Resistant Coatings New types of anti-corrosion coatings can be considered to protect high-performance fasteners.
Corrosion-Resistant Coatings This type of coating is eco- friendly, minimizing the use of heavy metal in fasteners.
Corrosion-Resistant Coatings In addition to corrosion resistance, the coatings lubricate threads, making fastener insertion and removal easier. Easier removal is a big plus when doing repairs, remodels, and retrofits.
Corrosion-Resistant Coatings The coatings can be pigmented to color-match other building materials or to simplify product identification.
Corrosion-Resistant Stainless SteelIt should be considered for critical structuralconnections and in locations with corrosiveenvironments.
Corrosion-Resistant Stainless SteelNote that even stainless steel requires a coatingfor protection against galvanic corrosion, as will bediscussed later in this course.
Galvanic CorrosionGalvanic corrosion occurs when dissimilarmetals, such as aluminum and steel, are incontact in the presence of an electrolyte, anelectrically conductive medium, and form agalvanic cell. H+ H+ H+
Galvanic CorrosionThese galvanic cells are similar to those inelectric batteries. In batteries, however, cells aresealed so galvanic reactions only occur when thecells are part of a controlled electrical circuit. H+ H+ H+
Galvanic CorrosionThe same reaction occurs in buildings when twopieces of metal form an uncontrolled short circuit.It occurs because of the electro-chemicalrelationship of the metals. H+ H+ H+
Galvanic SeriesCathode (Least Active) Metals conduct electricity Gold because they have a Silver Stainless Steel tendency to give up Bronze electrons easily. Copper Brass Nickel Some metals give up Lead Steel & Iron electrons more easily than Aluminum others. Zinc Magnesium Anode (Most Active)
Galvanic SeriesCathode (Least Active) They can be listed in order Gold of their potential to yield Silver Stainless Steel electrons, a table known as Bronze a Galvanic Series. Copper Brass Nickel Lead Steel & Iron Aluminum Zinc Magnesium Anode (Most Active)
Galvanic Series Cathode (Least Active) They can be listed in order Gold of their potential to yield Silver Stainless Steel electrons, a table known as Bronze a Galvanic Series. Copper Brass Nickel Lead Steel & IronLess “noble” Aluminum(sacrificial and Zincmore Magnesiumcorroded) Anode (Most Active)
Galvanic Series Cathode (Least Active) They can be listed in order Gold of their potential to yieldMore “noble”(protected and Silver Stainless Steel electrons, a table known asless corroded) Bronze a Galvanic Series. Copper Brass Nickel Lead Steel & IronLess “noble” Aluminum(sacrificial and Zincmore Magnesiumcorroded) Anode (Most Active)
Galvanic Series Cathode (Least Active) Aluminum is more active Gold (anodic) than steel orMore “noble”(protected and Silver Stainless Steel stainless steel.less corroded) Bronze Copper Brass Nickel Lead Where aluminum and steel Steel & Iron form a galvanic cell, AluminumLess “noble”(sacrificial and Zinc aluminum will corrode,morecorroded) Magnesium sacrificing electrons that will deposit onto and Anode (Most Active) protect the steel.
Galvanic CorrosionThis aluminum plate received two screws made from300-series stainless steel, a grade that is highlyresistant to oxidation and rusting.
Galvanic CorrosionIt was then exposed to 1000 hours of salt-water spraythat acted as an electrolyte to form a galvanic cellbetween the aluminum plate and stainless steelfasteners. The screws were them removed to allowexamination of the plate.
Galvanic CorrosionStainless Steel Stainless SteelScrew: Screw WithThe aluminum Anti-Corrosionsacrificed electrons Coating:to the steel. The Coating preventedsurface of the formation of aaluminum is visibly galvanic cell anddeteriorated. prevented corrosion of the aluminum plate.
Galvanic Corrosion Stainless SteelStainless Steel Screw WithScrew: Anti-Corrosion Coating:Using ordinary steel fasteners in architecturalaluminum elements (such as windows, curtain walls,or wall cladding) can create galvanic corrosion of thealuminum, weakening the connection until it fails atwell below design loads.
Galvanic Corrosion Stainless SteelStainless Steel Screw WithScrew: Anti-Corrosion Coating:Avoid this problem by specifying fasteners withhigh-quality anti-corrosive coatings.
Galvanic CorrosionDissimilar metalcombinations are commonin construction. Forexample:• Aluminum framed glazingunits and cladding getattached to structural steelframing using steel self-drilling, self-tapping screws.
Galvanic CorrosionDissimilar metalcombinations are commonin construction. Forexample:•Aluminum parts are oftenattached to concrete ormasonry with self-tappingscrews made of steel.
Galvanic CorrosionDissimilar metalcombinations are commonin construction. Forexample:•Even steel-to-steelconnections can involvedissimilar metals, if either ofthe steel parts, or thefasteners joining them, hasbeen coated with zinc.
Galvanic CorrosionThe Schermerhorn SymphonyCenter looks like solid stone,but it is clad with a thinveneer attached with self-drilling fasteners.
Galvanic CorrosionIt is difficult to prevent electrolytes from contactwith fasteners.Moisture can enter construction due to: –Rain or dew during Construction. –Condensation inside a wall or roof. –Leaks in building envelope –Water from building maintenance or operations. –Plumbing failures. –Flooding and spills. –Perspiration from workers that install the parts. –Air pollutants can make atmospheric moisture more conductive.
Galvanic Corrosion If dissimilar metals are in contact,assume that an electrolyte will also be in contact with the fasteners.
Galvanic Corrosion Specifying fasteners with adequate corrosion resistance protects againstcatastrophic failure, loss of use, injury, death, and liability.
HASCCThe Invisible Corrosion
HASCC The Invisible CorrosionHydrogen, a by-product of galvanic corrosion, can weaken standard fasteners and cause failure. It produces a type of corrosion that is not readily apparent…until it is too late.
A Case Study20 years after installation,screws began snapping forno apparent reason.The screws complied withbuilding code loadrequirements.While they had been exposedto weather due to roofdamage, they were not visiblycorroded.
A Case StudyThey simply appearedto have broken in half.
A Case StudyScanning electronmicrographs (SEM) revealedfractured fastener surfacesand separated grainboundaries in the steel. Thescrews had also lost ductility.
A Case StudyThe Culprit: HASCC!
Hydrogen Embrittlement HASCC starts with hydrogen embrittlement, which is associated with galvanic action. However, steel fasteners are not weakened by galvanic corrosion itself. Rather, hydrogen generatedScrews attacked by by galvanic action attacks thehydrogen embrittlementtypically show no visible steel.corrosion.
Hydrogen Embrittlement Even if steel is protected from galvanic corrosion, hydrogen can attack it rapidly. Specialized fasteners have been developed to avoid this risk.Screws attacked byhydrogen embrittlementtypically show no visiblecorrosion.
Source of Hydrogen1. Galvanic action creates electrical current.2. Water in electrolyte separates into oxygen and hydrogen. H+ H+ H+
Source of Hydrogen1. Oxygen bonds with anode and oxidizes metal. Oxides have little structural strength, the anode weakens and corrodes.2. Hydrogen is attracted to the cathode and penetrates into the metal. H+ H+ H+
Source of HydrogenThis process is similar to thelaboratory procedure forseparating water into hydrogenand oxygen by passing electricalcurrent through it, a processcalled electrolysis.
Hydrogen Diffuses into SteelHydrogen, the smallestatoms, can penetrate“solid” steel.Atoms lodge in voids insteel’s crystal structure. This scanning electron microscope (SEM) image of steel shows enlarged grain boundaries indicative of hydrogen embrittlement.
Hydrogen Diffuses into SteelSingle hydrogen atomsare unstable and bondwith other hydrogenatoms.The larger H2 molecules This scanning electron microscopeput pressure on the (SEM) image of steel shows enlarged grain boundaries indicative of hydrogensurrounding steel embrittlement.molecules.
Hydrogen Diffuses into SteelThis creates internaltension in steel, enlargingits grain boundaries andreducing ductility.The steel can no longer This scanning electron microscopebear its normal tensile (SEM) image of steel shows enlarged grain boundaries indicative of hydrogenload and becomes brittle. embrittlement.
The Role of Case HardeningCaseRockwellhardness Hydrogen has littleHRC 52 min. effect on “mild” (soft) steel. Many architecturalCore fasteners, however,Rockwell are case hardened.hardnessHRC 32-40
The Role of Case HardeningCaseRockwellhardness In case hardening,HRC 52 min. low-carbon steel is heated in a high- carbon environment to infuse extra carbonCoreRockwell into metal’s surface.hardnessHRC 32-40 This hardens steel’s outer layer (“case”) and makes it brittle.
The Role of Case HardeningCaseRockwellhardness Case hardeningHRC 52 min. makes self-drilling screws hard enough to drill and tap into structural steel or tapCoreRockwell concrete.hardnessHRC 32-40
The Role of Case HardeningCase HASCC affects steelRockwellhardness of Rockwell hardnessHRC 52 min. ≥ HRC 35. The harder the steel, the moreCore susceptible is it toRockwell HASCC.hardnessHRC 32-40 Case-hardened fasteners are typically HRC 52 on the case and HRC 32 to 40 in the core.
Hydrogen Embrittlement & Stress In case-hardened fasteners, only the brittle outer layer is vulnerable to HASCC. However, a weakening outer layer places the entire load onto the core of the fastener, a significantly smaller diameter of steel than the original design.
Hydrogen Embrittlement & Stress The design load can overwhelm this reduced fastener diameter, leading to failure.
Hydrogen Embrittlement & Stress This cross-section of a failed case-hardened fastener shows the hardened outer case, which was embrittled by hydrogen, and the inner ductile core, which failed under the design load.
Hydrogen Embrittlement & Stress A. Application Induced Hydrogen Assisted Stress Corrosion Embrittlement Mode B. Ductile and Embrittlement Mode/ Strength loss C. Complete ductile failure due to reduced cross- sectional area of fastener – unable to sustain application load.
Stress ConcentrationStress increases steel’s susceptibility to hydrogenembrittlement.Stress concentration occurs at screw heads for 3reasons:1. MANUFACTURING: Deformations required to form steelrod into screw heads induces stress into metal.
Stress Concentration 2. CLAMPING FORCES When screws are tightened, their heads bear on the surface of the object being attached. This places the area of the shank immediately under the head into tension, inducing stress.
Stress Concentration3. OUT OF ALIGNMENTScrew holes are rarelyperfectly perpendicular tothe surfaces they areattaching.When tightened, unevenpressure is put on thescrew’s head.This puts additional stresson one side of the fastenerat juncture of head andshank.
Stress ConcentrationA standard test forresistance to hydrogenembrittlement mimics thisreal-world situation.The fastener is screwedthrough two plates ofdissimilar metals. A shim isplaced under one edge ofthe top plate, creating anangle between the twoplates and placing the screwat an oblique angle withrespect to one of them.
Stress CrackingEmbrittlement at stress points leads to microscopiccracking.Micro-cracks further concentrate stress points.Once propagated, cracks can spread quicklythrough hardened steel.Metallurgists call this cracking “Hydrogen AssistedStress Corrosion Cracking” (HASCC).
Plating and HASCCCase hardened fasteners must still be protectedagainst rust and galvanic corrosion.Plating should not be used with most casehardened fasteners because the plating processgenerates hydrogen that contributes to HASCC.Instead, case hardened fasteners should beprotected with a high-performance anti-corrosioncoating or with new innovations such as thosedescribed in the next section.
HASCC Recap• Galvanic action between dissimilar metalsgenerates hydrogen.• Hydrogen penetrates steel and creates internalstresses that embrittle and weaken fasteners.• This process occurs primarily in case hardenedparts.• Stress concentrations initiate micro-cracking thatcan propagate across fastener.• HASCC can occur years after fastener installationif connection is exposed to moisture.• Failure is often sudden and without warning.
The Remedy for HASCCSelf-Drilling Fasteners have to be casehardened in order to drill and tapsubstrates – but case hardening makesthem vulnerable to failure.Fortunately, there is a solution to fastenerHASCC hazards.
Benefits of Self Drilling ScrewsWhy use self-drilling screws?Self-drilling screws require just a fewpercent of installation time and Installed with screw gun.labor required by nuts-and-bolts,rivets, and other fasteners requiringpre-drilled holes.Fasteners install in single, fastoperation using a power driver.
Benefits of Self Drilling ScrewsThey are much faster thantwo-handed bolt-and-nutinstallations, and morepractical where the backside is not accessible forinstalling a nut.With hundreds of thousandsof fasteners used in largebuildings, this representsan enormous savings in labor.
Benefits of Self Drilling ScrewsUse to install windows, cladding,curtain wall, framing, anchors,equipment, fixtures, and otherbuilding components. Substrate becomes the nut
Design of Self Drilling Screws Select head for easy installation,Attaching into Metal: Lead threads acceptable profile, and pull-overtap threads into substrate, so the resistance.substrate acts as a nut without Select threadrequiring the time to tighten a nut. style to hold in substrate.They are available in manyspecialized configurations to suit awide range of construction Lead threads cut threadsapplications. into (tap) substrate for pull-out resistance. Tip drills hole and removes shavings.
HASCC-Resistant FastenersHigh performance structural drill screws:Lower hardness (HRC 28-34)Load-bearing threads for ductilityVirtually immune to embrittlementfailures.Increased hardness (HRC 52 min)point and lead threads for drillingand tapping
HASCC-Resistant FastenersHigh performance structural drill screws:Lower hardness (HRC 28-34)Load-bearing threads for ductility Vir tuVirtually immune to embrittlement all to y Im HA mfailures. SC un C eIncreased hardness (HRC 52 min)point and lead threads for drillingand tapping
A Metallurgical MarvelThere are two ways to achieve this performance:2. Selectively Hardened Fasteners3. Bi-Metal Fasteners Hardened for Ductile for structural performance drilling and tapping. and HASCC-resistance.
1. Selectively Hardened Fasteners Selectively hardened fasteners are made from DUCTILE WHERE special, high-carbon NEEDED steel. Since the alloy already contains the carbon HARDENED needed to harden the WHERE NEEDED steel, fasteners do not have to be placed in a high-carbon environment during heat treatment.
1. Selectively Hardened Fasteners This makes it possible to selectively harden DUCTILE WHERE fastener tip. NEEDED The tip of the screw is passed through an electrical induction coil HARDENED that heats and hardens WHERE NEEDED drill-point and lead- threads without affecting the rest of the shank.
2. Bi-Metal FastenersUse where stainless steelis required for increased Stainlessresistance to corrosive Steel Headenvironments. and Shank High-Carbon Steel Tip, Selectively Hardened Recommended for exposed fasteners.
2. Bi-Metal FastenersStainless steel is notsuitable for selective Stainlesshardening. Instead, a high- Steel Headcarbon steel tip is fused and Shankonto a stainless shank. High-Carbon Steel Tip, Selectively Hardened Recommended for exposed fasteners.
2. Bi-Metal FastenersThe high carbon tip is thenselectively hardened Stainlessusing induction-coil Steel Headheating. and Shank High-Carbon Steel Tip, Selectively Hardened Recommended for exposed fasteners.
Corrosion-Resistant CoatingsEven stainless steel is not immune to galvaniccorrosion and the elements.Non-metallic, anti-corrosion coatings arerecommended on both selectively hardened and bi-metal fasteners to provide additional protection andlubricate the threads. Bi-Metal Fastener: Before coating, above. After coating, below.
Corrosion-Resistant Coatings Bi-Metal Fastener: Before coating, above. After coating, below.Coating can be color matched as required.
PROOF Steel and aluminum plates are connected by fasteners and sprayed with saltwater, an electrolyte. HASCC- resistant fasteners are not affectedStandardcase-hardenedfasteners failed
PROOF Conventional fasteners fail due to stress concentration at screw heads that accelerates embrittlement. HASCC- resistant fasteners are not affectedStandardcase-hardenedfasteners failed
PROOF Neither selectively-hardened nor bi-metal fasteners fail. HASCC- resistant fasteners are not affectedStandardcase-hardenedfasteners failed
US Bank BuildingLos Angeles, CAPei Cobb Freed Partners PROOF HASCC-resistant fasteners, securing roof- top panels and building envelope, have been exposed to marine and urban atmosphere and earthquakes during two decades of service.
Best Industry PracticesIn applications wheredissimilar metals will be incontact, specifyselectively-hardened self-drilling fasteners to resistHASCC.
Best Industry Practices In aggressive environments requiring stainless steel for protection against visible corrosion, specify bi-metal self-drilling fasteners with a selectively-hardened tip to resist HASCC.
FASTENERS FOR EXTREME LOADS Fasteners exposed to extremeloads also require special attention to HASCC.
Extreme Loads• During extreme loading, structures are briefly subjected to loads far higher than normal operating loads. Determination Estimate Risk-Resistant of Risk of Risk Loads Design
Extreme Loads• Risks can include: • Hurricane & Tornado, including windblown missile impact • Earthquakes • Accidents (industrial accident, vehicular collision, etc.) • Redistribution of load due to failure of other building elements • Explosion, including boiler, natural gas leaks, & attacks. Determination Estimate Risk-Resistant of Risk of Risk Loads Design
Extreme Loads• If there is reason to suspect a risk, it should be designed for. Determination Estimate Risk-Resistant of Risk of Risk Loads Design
Hurricane and Tornado LoadsUse building codes and regional history to predictloads.
Hurricane and Tornado Loads High-speed winds create extreme atmospheric pressure differentials between the interior and exterior of building enclosures. High-velocity, windblown missiles create extreme impact loads.
Blast (Explosion) LoadsBlast resistance should bedesigned into structures:•Containing volatilematerials.•With high-security profile.•With strategic importance The attack on Oklahoma City Federal Building provoked rethinkingto an organization or of the need for blast-resistance.mission.
Blast (Explosion) LoadsBlast resistance should bedesigned into structures:•That are or have occupantsconsidered targets forattack.•Located near possible The attack on Oklahoma Citytargets. Federal Building provoked rethinking of the need for blast-resistance.
Blast (Explosion) LoadsBlast resistance should bedesigned into structures:•That are “EssentialFacilities” that must remainfunctional after disastersdue to importance to public The attack on Oklahoma Cityhealth and safety: Federal Building provoked rethinking of the need for blast-resistance. • Hospitals • Fire/rescue/police stations • Toxic-material storage • Air traffic control • Critical defense installations.
Extreme Loading-Building EnvelopeHurricane, tornado andexterior blast loads areapplied first to buildingcladding and fenestration.These elements eitherabsorb the load - bydeformation or failure - ortransfer load to otherstructural elements.
Seismic Loading Violent, cyclical accelerations place extreme loading on all building components, not just structural members. Failures of non- structural elements can injure or kill people and make buildings unusable.
Extreme Loading of FastenersUnder extreme loading, if astructural element does not fail, andit does not deform sufficiently toabsorb all the load energy – that is,if it is designed to withstand theload – then the load is transferredto the fasteners that hold it in placeand connect it to other structuralelements.
Extreme Loading of FastenersIf the fasteners are ductile innature, they will deform, absorbingsome or all of the blast or impactenergy, but may still keep in placethe element they are attaching.If fasteners are brittle, extremeloading may cause them to fail.
Case-Hardened & Extreme LoadsThe outer layer of case- Hardenedhardened fasteners is brittle (brittle)and less ductile. case Core diameter < fastener diameterUnder extreme loads, the Softbrittle outer case fails first, (ductile)leaving the inner core to bear coreload. Cross-section of case-hardened fastener.
Case-Hardened & Extreme LoadsEven though the core may be Hardenedductile, its smaller area can (brittle)becomes overloaded and fail. case Core diameter < fastener diameterFasteners with incipient SoftHASCC are even more likely (ductile)to fail during extreme loading. core Cross-section of case-hardened fastener.
Case-Hardened & Extreme LoadsUsing ductile, HASCC- Hardenedresistant fasteners helps (brittle)assure full design strength case Core diameter <of fasteners can be used to fastener diameterresist extreme loads. Soft (ductile) core Cross-section of case-hardened fastener.
Where to Specify•Blast resist windows.•Curtain wall framing.•Building equipment.•Critical life safety andcommunicationsequipment.
OTHER TYPES OF FASTENERS HASCC-resistant fasteners can be used to simplify a wide range of special construction applications.
Concrete and Masonry Screws Specifying concrete and Choice of masonry anchors head styles also requires consideration of dissimilar metals and corrosion resistance. Hi-Lo thread taps into masonryConcrete Masonry
Concrete and Masonry Screws A variety of special Choice of head designs are styles available to satisfy most construction requirements. Hi-Lo thread taps into masonryConcrete Masonry
Pressure-Relief FastenersIn buildings withpotential for interiorexplosions, specialpanels can bedesigned to blow offand relievepressure, a built insafety valve.
Pressure-Relief FastenersExamples includeplaces where highlyvolatile liquids are inuse, or storage forextremely fine, drymaterials subject todust-explosion.
Pressure-Relief FastenersPressure-reliefpanels are notactually held in placeby fastener heads.Panels have anattachment-holelarger than thefastener-head, anda special aluminumwasher retains thepanel in position.
Pressure-Relief FastenersUnder explosivepressure, washersfail and allow panelsto blow off, ventingthe pressure.The panel is looselytethered to keep itfrom becoming adangerous missile.
Pressure-Relief FastenersHASCC-resistantfasteners can beused in assembly.
Threaded Rod AnchorsThreaded rods are used to support fire sprinkler, HVAC, refrigeration,general piping, electrical systems, and other essential buildingservices.Self-tapping, self-drilling anchors simplify installation of these rods.
Sealing WashersHigh performancewashers helpprevent leaks in thebuilding envelope.
SUMMARY• Fasteners are critical components of buildings.• Architects and Engineers must be aware of their professional responsibility to specify fasteners that fulfill design intent and provide safe and durable connections.
HASCC-Resistance• HASCC can cause sudden, catastrophic failures when self-drilling or self-tapping screws are used in conditions with dissimilar metals and the potential for exposure to moisture.• It is not safe to assume that contractors will be aware of this issue and will select anything other than standard fasteners. Specify accordingly.• Selectively hardened and bi-metal self-drilling fasteners mitigate risk because their load- bearing sections remain ductile and less vulnerable to HASCC.
Economy• The lowest cost fastener may not be the most economical when labor and service life are considered.• Specialty fasteners can sometimes save money by providing lower installed cost.• Fasteners are less than 2% of total building cost, but specifying inadequate fasteners can cause up to 100% of construction defect costs.
Sustainability• Most metal fasteners have recycled-material content and are recyclable.• New corrosion-resistant finishes eliminatetoxic heavy metal plating.• Durability over the life of a structure is themost important measure of sustainability.
Thank you!This concludes the American Institute of Architects Continuing Education Systems Program. Any Questions?Gregg Melvin, Elco Construction Products(815) 979-3249 - email@example.com