Concrete Breakout Capacity Of Cast-in-place Concrete .
Concrete breakout capacity ofcast-in-place concrete anchorsin early-age concreteJames B. Winters and Charles W. DolanP Precast concrete elements are often stripped at strengths lowerthan the minimum 2500 psi (17 MPa) required by ACI 318-08appendix D, raising a concern as to whether the ACI equationsare applicable for early-age concrete. Seventy-eight pullout tests were conducted on headed studassemblies in concrete as young as 12 hours. The results indicate that the tensile strength of early-age concrete rises faster than the compressive strength, and the pullout strength of the inserts exceeds the capacity predicted byACI 318-08 and the sixth edition of the PCI Design Handbook:Precast and Prestressed Concrete for compressive strengths aslow as 1000 psi (7 MPa).114W int e r 2 0 1 4 PCI Journalrediction models for the breakout strength design ofinserts were developed using mature concrete with aminimum concrete compressive strength of 2500 psi(17 MPa). Inserts used in stripping precast and prestressedconcrete and tilt-up construction may see loads applied asearly as 18 hours after casting, and architectural elementsmay have stripping and handling loads applied even earlier.There are anecdotal reports of failure of stripping insertsat these early ages. There are multiple potential reasonsfor these failures. First, the failure can occur due to theintricacies of the individual lifting device. Second, if thetensile capacity of the concrete develops more slowly thanthe compressive strength and decisions are based on compressive strength, a premature failure may occur. Third, ifthe insert is designed for the specified concrete strengthrather than the stripping strength, there may be insufficientembedment. Fourth, stripping requirements may not haveincorporated suction or dynamic loads due to stripping andhandling. Increases in loads from stripping and handlingare not considered in this study but must be considered inplant operations.Research significanceThe objective of this research is to determine, theoreticallyand experimentally, whether the current concrete breakoutstrength models based on concrete compressive strength
and embedment depth for mature concrete can be appliedto early-age concrete, specifically, whether at early age thebreakout capacity is properly modeled using the compressive strength or whether an early-age correction factor isneeded. Breakout failure is influenced by the tensile andcompressive strength of the concrete, the variability of theconcrete strength at early age, and the possible additionalloads imposed in stripping the concrete from the form anddynamic effects during handling.BackgroundEarly-age concrete tensileversus compressive strengthThe correlation between tensile and compressive strengthis critical to this project because of the emphasis on earlyage performance. While the concrete tensile strength affects breakout capacity of the anchor, compressive strengthis most commonly measured and reported. In the literaturereview, the compressive strength is the variable mostcommonly used in predicting breakout strength and theconcrete tensile strength is often not reported.Although sometimes it is unclear in the published research whether it is the mature compressive strength or thestrength at the age of the concrete testing that determinesa concrete’s tensile strength, the relationship between thetwo appears to be that as the compressive strength increases so, too, does the tensile strength, but at a decreasing rate.Many of the equations for comparing tensile and compressive strength are presented and used for comparison withthe values obtained in this research.Neville1,2 explains the difficulties in developing a directrelationship between concrete compressive and tensilestrengths. Neville lists at least six different factors that affect the concrete tensile strength–to–compressive strengthratio ft/fc. These factors include the strength, coarse andfine aggregates, age, curing, air entrainment, and densityof the concrete. Aggregate can affect strength becausecrushed coarse aggregate increases flexural strength. Thefine aggregate affects the ratio based on the aggregategrading, and possibly because of the difference in surfaceto-volume ratio in the specimens used to measure compressive and tensile strength when modulus of rupture istaken as the tensile strength. The effects of age are onlydiscussed beyond an age of one month, at which point thetensile strength increases more slowly than the compressive strength, which is similar to the overall tendencyfor the ratio of ft/fc to decrease as compressive strengthincreases. Curing affects the ft/fc ratio because tensilestrength is more sensitive to shrinkage during dry curingin flexure test beams. Air entrainment lowers the compressive strength more than the tensile strength. Lightweightconcrete may have high ratios of ft/fc at low strength, but athigher strengths the ratio is similar to that of normalweightconcrete. Drying may reduce the ratio for lightweightconcrete by 20%.Mindess, Young, and Darwin3 present the same factorsaffecting the ratio of concrete compressive strength totensile strength as Neville. In addition, they explain howdifferent tensile test methods produce different ratios. Theratio of splitting tension to compressive strength is usuallyin the range of fsp/ equal to 0.08 to 0.14 (where fsp is thesplitting tensile strength, andis the specified concretecompressive strength at 28 days). However, the ratio ofdirect tensile strength to compressive strength is about 0.07to 0.11, and the ratio of modulus of rupture to compressivestrength is about 0.11 to 0.23.Equation (1) is used by ACI 318-084 as a lower bound.psi (MPa)(1)The following equation is proposed by ACI Committee 363.5psi (MPa)The following best fit of the data is proposed by Mindess,Young, and Darwin.psi (MPa)This best fit equation is in general agreement except thebest fit exponent is larger than the ½ proposed by ACI 31808.Oluokun et al.6,7 state that the ACI 318-08 exponent of ½is not valid for early-age concrete. Oluokun et al. testedthree laboratory-prepared test mixtures and one samplefrom a precast, prestressed concrete producer. The 28-daycompressive strengths ranged from 4000 to 9000 psi (28 to62 MPa) for the four mixtures. Standard 6 12 in. (150 300 mm) cylinders were cast from a single batch for eachseries of testing. The coarse aggregate for all mixtures was90% to 100% retained on a ¾ in. (19 mm) sieve with 100%less than 1 in. (25 mm). The fine aggregate was a manufactured crushed limestone aggregate. Oluokun et al. concluded that crushed aggregate produced a tensile strengthabout 25% higher than smooth aggregate. Equation (2) isthe recommended formulation for tensile strength.psi (MPa)(2)Khan et al.8 selected modulus of rupture as the measureof the tensile strength. Three different curing conditionswere investigated, including temperature-matched curing,sealed curing, and air-dried curing. The three concretesconsisted of a nominal 4300; 10,150; and 14,500 psi(30, 70, and 100 MPa) compressive strength at 28 days.Khan et al. concluded that ACI 318-08 overestimates thePCI Journal Wi n t e r 2014115
32.5ACI 318-08ft /ft,2821.51Oluokun Eq. (2)0.5000.20.40.60.811.21.4f'c /f'c,28Figure 1. Normalized strength gains for early-age concrete. Note: ft concrete tensile strength; ft,28 28-day tensile strength of concrete.modulus of rupture for concrete compressive strengths lessthan 2180 psi (15 MPa) and underestimates it for strengthsabove 2180 psi (15 MPa). Further, Khan suggests thatACI 363R-92 overestimates the modulus of rupture fornearly all types of concrete.One hundred and eighteen 4 4 20 in. (100 100 500 mm) specimens were cast using various concretemixture proportions.9 Twenty specimens were made foreach of the ordinary portland cement concretes and ninespecimens for each of the 70% slag cement replacementconcrete and the 30% fly ash replacement concrete. Fifteenof the twenty specimens were tested at the ages of 1, 3, 7,14, and 28 days at a strain rate of 5 µε/min. The remaining five were tested at 28 days at different strain rates.Three were tested at a strain rate of 1 µε/min and two at30 µε/ min. The nine specimens of fly ash and slag-cementconcretes were tested at 7, 14, and 28 days at a strain rateof 5 µε/ min. The compressive strength was measuredusing three 4 in. (100 mm) cubes at each age. Embeddedsteel bars were used to apply the load. Khan et al. concluded that the tensile-to-compressive strength ratio decreasesas concrete matures and the tensile strength gain is similarfor a wide variety of mixtures.From this review, it is concluded that the tensile strengthincreases faster than compressive strength at early agewhen compared with the corresponding strength gainsof mature concrete. This is determined from the higherslope of the tensile-to-compressive strength graph atearly ages. Prediction methods used by ACI 318-08,and by extension the PCI Design Handbook: Precastand Prestressed Concrete,10 underestimate modulus ofrupture at compressive strengths greater than 2180 psi(15 MPa). Many of the models presented in the literaturereview were used for comparison with the data presented in this report.116W int e r 2 0 1 4 PCI JournalFigure 1 examines the ratio of tensile strength gain tocompressive strength gain. Both the tensile and compressive strengths are normalized to the 28-day strength fora 5000 psi (35 MPa) concrete. The ACI 318-08 equation(Eq. [1]) and the Oluokun equation for early-age concrete(Eq. [2]) are compared. Oluokun predicts a lower initialtensile strength than the ACI 318-08 formulation, which isconsistent with Khan’s findings. In both cases, the initialtensile capacity gain is higher than the compressive capacity. Thus, experimental validation should result in tensilestrength gains on the order of 30% to 50% more than compressive strength gains based on Oluokun’ s hypothesis.Theoretically, then, the inserts should perform well at earlyage. Table 1 summarizes the model equations evaluatedfor tensile capacity.A full analysis of this research complete with the proposedstrength equations for both concrete tensile strength andinsert breakout capacity is presented in Concrete BreakoutCapacity of Cast-in-Place Anchors in Early AgeConcrete.11Breakout strength of headed studsA review of the development of the breakout strength ofheaded stud inserts provides an evolution of predictivemodels over time, ultimately leading up to models currently used in practice. The models used for comparison inthis paper are the models presented by Anderson, Tureyen,and Meinheit12 and in the sixth edition of the PCI DesignHandbook.The PCI Design Handbook and ACI 318-08 present characteristic capacities based on a 5% fractile. A 5% fractile isdefined as a 90% confidence that there is a 95% probabilityof the actual strength exceeding the nominal strength. Thisfractile is calculated by Eq. (3):
Table 1. Summary of tensile strength modelsSourceft , psift , MPaCEBOluokunACI 318-08ACI 363-92Mindess, Young, and Darwin best fitOluokun, 6 hours and 5 MPaOluokun, 5 MPaKhan (open)Khan (sealed)Khan (dry cured)Note: Winters and Dolan 2013 provide a complete comparison of tensile strength comparisons. fc concrete compressive stress; specified concrete compressive strength at 28 days; fr modulus of rupture; fsp splitting tensile strength; ft concrete tensile strength; t time.F5% Fm(1 – Kν)(3)PCI Design Handbook. This approach is similar to punching shear calculations for a slab around a column.whereF5% 5% fractile or characteristic capacityFm mean failure capacityK factors for one-sided tolerance limits for normaldistributionsν coefficient of variationThis approach is used for comparison with the equationspresented in ACI 318-08 and the PCI Design Handbook.Design models for connections inprecast and cast-in-place concreteCourtois13 described problems with testing using smallblocks that resulted in flexural splitting failure of the blockbefore the ultimate capacity of the insert was reached. Inaddition, tests conducted at this time showed both concretecompressive strength and embedment depth to be important parameters for determining pullout capacity.A shear cone breakout failure occurs where a concrete conedefined by the depth of embedment of the insert fails inshear. This is the type of breakout failure that was presented as a simple model and was used in early editions of theCourtois identifies split cylinder tests as more informative than compression cylinder tests. He suggested that thebreakout strengths might be more closely predicted whenthe concrete tensile strength is known than when only theconcrete compressive strength is known. Courtois listsan area of future research: “In mass concrete structures,we must learn more about the ultimate tensile strength ofconcrete at very early ages. Forms are usually reanchoredto a previous lift at ages of 48 to 72 hr and safe anchoragemust be assured.”Sattler14 reports the pure tension strength of connectorshaving headed studs based on a conical failure modemodel. Sattler proposes a global safety factor equivalent toa load factor divided by a corresponding strength reductionfactor of 2.0 to derive an allowable load. Sattler’s work didnot address spacing requirements of groups, edge-distanceallowances, or anchoring to concrete in the tensile zone ofa member where cracks could exist.Bode and Roik15 recommend design formulas for singlestuds loaded in tension based on cube strengths and thesquare root of the embedment length. They also note thatfor shorter studs, 2 in. (50 mm) in total length after welding, the standard deviation is greater than for longer studsbecause of the nonhomogeneous composition of the surrounding concrete and the close distance between the studhead and the concrete surface. Bode and Roik recommendPCI Journal Wi n t e r 2014117
reducing the strength by 20% for shorter studs. No furtherrecommendations on other lengths are discussed.wherea curve-fitting coefficient for concrete strength effectHawkins16 conducted 12 tests on 1 in. (25 mm) diameteranchor bolt breakout specimens in 20 MPa (3000 psi) concrete. Embedment depth varied among 3, 5, and 7 in. (75,125, and 175 mm). The washer diameter below the boltvaried among 2, 4, and 6 in. (50, 100, 150 mm). The thickness of this washer also varied as either 5 8 or 7 8 in. (16 or22 mm). Nine specimens were 18 in. wide 18 in. long 9 in. deep (450 450 225 mm) and reinforced nearthe edges. The other three specimens were 46 in. wide 46 in. long 7 in. deep (1150 1150 175 mm) and alsoreinforced near the edges.Hawkins’s loading frame reacted against the concrete with18 in. long 2 in. wide (450 mm 50 mm) steel beamswith 16 in. (400 mm) center-to-center spacing for thesmaller blocks and 30.5 in. long 5 in. wide (760 mm 125 mm) steel beams with 41 in. (1025 mm) center-to-center spacing for the larger block. Load was applied througha 100-ton (996 kN) center-hole ram positioned over a loading rod attached to the bolt.Only three specimens showed conical breakout failures:one from the smaller block tests and two from the largerblock tests. The reason presented for this is that the moment generated by the testing frame induces flexural cracking in the concrete, causing radial cracking failure beforeconical breakout failure can be reached. This is similar tothe problems listed by Courtois, that is, a majority of thefailures were splitting of the concrete.From Hawkins’s conclusions, an embedment depth of 8 to10 times the bolt diameter is required for ductile behavior.Splitting failure is likely to occur when the embedmentdepth–to–bolt diameter ratio exceeds 4. Also, anchor boltsare likely to have ultimate capacities 20% to 30% less thancomparable sized headed stud connectors.Headed anchor breakout behaviorin tensionb curve-fitting coefficient for effective embedment depthα breakout strength coefficients determined by testinghef effective embedment depth of insertβ breakout strength coefficient determined by testingRegression analysis shows an excellent concrete breakoutprediction equation using the variablesand hef. Thecorrelation coefficient R2 value is nearly 0.98. The regression analysis shows the magnitude of the breakout strengthcoefficient α to consistently be about 1/2 forand β tobe 3/2 for hef. Adding the variables for stud head diameterand stud shaft diameter did not significantly increase theR2 value. These equations were developed usingof thecylinder equal to 0.85fcube,200 as the correlation betweencylinders and cubes.ACI 318-08 appendix D assumes an average predictionequation for headed cast-in-place anchors in uncrackedconcrete Nu,ACIheaded (Eq. [4]):lb(N)(4)This equation is used throughout this paper for comparison with the data collected and is equivalent to theequation presented in ACI 318-08 and the sixth edition ofthe PCI Design Handbook. This gives a test-to-predictedratio of 0.992. However, when the cube strength conversion factor3 of 1.11 is used, the test-to-predicted ratioincreases to 1.11. Using the concrete strength conversionvalues from CEB-FIB, Eq. (5) is the PCI Design Handbook average prediction equation for headed cast-in-placeanchors in uncracked concrete Nu,PCIheaded.lbA database was assembled on tension testing when the concrete capacity design method was in development.12 Mostof the data used 200 mm (8 in.) cube crushing strengthfcube,200. Using this information, they concluded that no additional tension testing was needed to describe the behavioral characteristics of welded headed stud anchors loadedin direct tension.(N)(5)Another ACI 318-08 alternative equation is presented foranchors with deep embedment, that is, hef greater than12 in. (300 mm):lbThe tensile breakout strength N prediction takes the generalform of the following equation:(N)The fifth edition of the PCI Design Handbook17 still usedinformation based on Courtois’s work, that capacity is pro-118W int e r 2 0 1 4 PCI Journal
portional to, which overpredicts the test data by 16% to30% depending on the strength conversion.From regression analysis of tension data assumingequals 0.85fcube,200, Eq. (6) is the best fit equation.lb( N)(6)Anderson, Tureyen, and Meinheit note that a conversionfactor for cubes of different sizes was taken as:Figure 2. Example stud assembly.Headed steel stud anchorsin composite structures:Tension and interactionAs the use of composite construction increases, conditions that lead to tension and combined shear and tensionin headed studs are more prevalent. Examples include infillwalls, coupling beams, connections to composite columns, orcomposite column bases. Pallares and Hajjar18 note that themost advanced information on headed studs is included in thesixth edition of the PCI Design Handbook and ACI 318-08.Composite design research considered only tests withno edge effects and concrete strength greater than 3 ksi(20 MPa). The 3 ksi limit is the minimum strength permitted by the American Institute of Steel Construction forcomposite structures. Based on the work presented byPallares and Hajjar, concrete breakout is prevented if hef isgreater than 7.5d (where d is the diameter of split cylinderor headed stud). This gives values similar to the 8 to 10values proposed by Hawkins.16Anchor strength test programThe equations in the sixth edition of the PCI DesignHandbook for concrete breakout of headed studs are basedon mature concrete values. In the precast concrete industry,loads for stripping, lifting, and handling are applied beforeconcrete reaches full maturity. There is little research onthe effects of early concrete age on breakout strength asopposed to 28-day low-strength concrete. The test protocolfollows ASTM E48819 and is conducted in uncracked concrete, as would be expected for stripping and handling ofnewly cast precast concrete panels. ACI 355.2-0720 criteriaare fo
the concrete tensile strength is known than when only the concrete compressive strength is known. Courtois lists an area of future research: “In mass concrete structures, we must learn more about the ultimate tensile strength of concrete at very early ages. Forms are usually reanchored to a previous lift at ages of 48 to 72 hr and safe anchorage
To create breakout groups, open Collaborate Panel, click Share Content tab, and select Breakout Groups. In breakout groups, each participant has a presenter role, so they can share content, and use whiteboard. After selecting Breakout Groups, you have two options for assigning the groups that are randomly assign
Expansion Anchor (Hammer Drive Anchor) A pull-out test was conducted to find out the tensile capacity. There are possibilities on failures or damages that can happen, one of them is concrete breakout [5]. Concrete breakout happens due to over pull-out capacity into the concrete, so that it is damaged or broken and raise upwards [10].
Redi-Mix Concrete, LLC 10K11521 . While EPDs can be used to compare concrete mixtures, the data cannot be used to compare between construction products or concrete mixtures used in different concrete products unless the data is integrated into a comprehensive LCA. For example, precast concrete, concrete masonry units and site cast concrete all .
examines the requirements of LEED v4 for BD C: New Construction and its relevance to cast stone. THE USE OF CAST STONE . Cast stone is used primarily on the exterior of buildings. Cast stone veneer may be used alone or as an integral part of a clay or concrete masonry veneer. Cast stone may also be used as an accent or trim material on the .
User Manual Rev. 1.1 — 4 February 2019 4 of 14 NXP Semiconductors LPC845 Breakout User Manual 2. Board Layout Figure 2 below shows the layout of the LPC845 Breakout board, indicating location of jumpers, buttons and connectors/expansion options. Table 1 below shows the layout of the LPC845 Breakout board, indicating location of
Breakout Rooms Breakout rooms allow the Host to split the Zoom meeting in up to 50 separate sessions. Breakout room participants will have the same audio, video, and screen share capabilities as allowed in the main ses
1.3.1 Concrete cast in situ and precast concrete (ordinary concrete) Cast-in-site concrete is an unhardened state, like ready-mix, and is placed in molds. Ready mixed concrete is proportioned and mixed off the pro
Cover illustration: Ballyaghagan Cashel, looking north-east . Centre for Archaeological Fieldwork, QUB Data Structure Report: AE/11/110 Ballyaghagan Cashel, County Antrim 3 Contents page List of figures 4 List of plates 4 Summary 5 Introduction General 6 Background 6 Reason for excavation and research objectives 7 Archiving 7 Credits and acknowledgements 7 Excavation Methodology 8 Account of .
