Pp06_ Asep_ Nscp 2015 Update on Ch4 Structural Concrete Part 1

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LECTURE SERIES ON THE UPDATES OF THE

NEW STRUCTURAL CODE OF THE

PHILIPPINES, VOL. 1 Buildings, Towers

and other Vertical Structures, 7

thth

Edition

PART 1:

CHAPTER 4, STRUCTURAL CONCRETE

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3

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3

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Structural Concrete, Chapter 4 of the National

Structural Code of the Philippines, Vol. I, 6

thth

Edi

Edition,

tion, 2010

2010 (NSCP),

(NSCP), was

was based on

based on ACI

ACI 318 ‐08.

318 ‐08.

Currently, the latest edition is ACI 318 ‐14. Prior

to its publication, experts and stakeholders in

the U. S. stated that the reorganization of this

standard will be

"monumental“

, with major

changes expected in the forthcoming edition.

We have used the ACI 318M ‐14 as the basis for

NSCP 2015 Vol. 1, Chapter 4, Structural

Concrete. The first printing of NSCP Vol. 1 (C101‐

15) was launched on Dec. 7, 2016.

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This will make the latest Chapter 4, Structural

Concrete of the National Structural Code of the

Philippines, Vol. I, 7

thth

_{Edition, (NSCP 2015) up to}

date. Our NSCP 2010 was based on ACI 318M ‐

08, the current edition at the time of NSCP 2015

Vol. 1 inception was ACI 318M ‐11. However we

have

have decided to

decided to use the

use the draft

draft version

version of

of ACI

ACI

318R ‐14 which was published in May 2014 as

our guide. We have subsequently updated our

final draft when ACI 318M‐14 was published in

March 2015 as the basis for NSCP 2015, Chapter

4. We were able to meet our Dec. 2016 target

because we have encoded the changes earlier &

encoded the few corrections later.

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REORGANIZATION OF NSCP 2015, 7th Edition, in accordance with ACI 318M‐14

NSCP 2015, 7th Edition, Chapter 4 NSCP 2010, 6th Edition, Chapter 4 Description Section Remarks Section

of Provisions and Title and Title Part 1: General 401 – General 401 – General

402 ‐ Notation and Terminology 402 – Definitions

403 ‐ Referenced Standards 403 – Specifications for Tests and Materials 404 ‐ Structural System Requirements New

Part 2: Loads and Analysis

405 – Loads 410 ‐ Flexure and Axial Loads

406 ‐ Structural Analysis 408 ‐ Analysis and Design Considerations Part 3: Members 407 ‐ One‐Way Slabs

408 ‐ Two‐Way Slabs 413 ‐ Two‐Way Slab Systems 409 – Beams

410 – Columns

411 – Walls 414 – Walls 412 – Diaphragms New

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of Provisions and Title and Title

414 – Plain Concrete Intact 422 – Structural Plain Concrete Part 4: Joints,

Connections, Anchors

415 – Beam‐Column and Slab‐Column Joints 416 – Connections Between Members

417 – Anchoring to Concrete Intact 423 – Anchorage to Concrete Part 5:

Earthquake Resistance

418 – Earthquake‐Resistant Structures Intact 421 ‐ Earthquake‐Resistant Structures Part 6:

Materials and Durability

419 – Concrete: Design and Durability Requirements 408 ‐ Analysis and Design Considerations 420 – Steel Reinforcement Properties, Durability,

and Embedments 412 – Development and Splices of Reinforcement Part 7: Strength

& Serviceability

421 – Strength Reduction Factors 426 – Alternative Load and Strength Reduction Factors 422 – Sectional Strength

423 – Strength‐and‐Tie Models Intact 427 ‐ Strength‐and‐Tie Models

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of Provisions and Title and Title Part 8:

Reinforcement

425 – Reinforcement Details 407 – Details of Reinforcements Part 9:

Construction 426– Construction Documents and Inspection

427 – Strength Evaluation of Existing Structures Intact 420 – Strength Evaluation of Existing Structures Part 10:

Evaluation 428 – Building Code Requirements for Concrete Thin Shells

Separate Publication ACI 318.2‐14

419 – Shells and Folded Plate Members Design 429 – Alternative Design Method

Adopted from previous NSCP Editions

424 ‐ Alternative Design Method References and

Appendices

Appendix A – Steel Reinforcement Information, WRI

Standard Wire Reinforcement (Customary & Metric) Included in Section 407 Appendix B – Equivalence between Customary U.S.

Units, SI Metric, MKS Metric

Appendix A Conversion Factors (similar to Appendix B of NSCP 2015, but not yet updated to the latest ACI 318M‐14)

No longer exist as

Separate sect. 416 – Precast Concrete No longer

exist as

separate section

418 ‐ Prestressed Concrete Discontinued

425 ‐ Alternative Provisions for Reinforced and Prestressed Concrete Flexural and Compression Members

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Chapter 4 – STRUCTURAL CONCRETE

First Printing, Dec. 2016

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Chapter 4 ‐ CONCRETE

401 GENERAL REQUIREMENTS

402 NOTATION AND TERMINOLOGY

403 REFERENCED STANDARDS

404 STRUCTURAL SYSTEM REQUIREMENTS

405 LOADS

406 STRUCTURAL ANALYSIS

407 ONE‐WAY SLABS

408 TWO‐WAY SLABS

409 BEAMS

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Chapter 4 ‐ CONCRETE

410 COLUMNS

411 WALLS

412 DIAPHRAGMS

413 FOUNDATIONS

414 PLAIN CONCRETE

415 BEAM‐CONCRETE AND SLAB‐

COLUMN JOINTS

416 CONNECTION BETWEEN MEMBERS

417 ANCHORING T0 CONCRETE

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Chapter 4 ‐ CONCRETE

419 CONCRETE DESIGN AND DURABILITY

REQUIREMENTS

420 STEEL REINFORCEMENT PROPERTIES,

DURABILITY REQUIREMENTS

421 STRENGTH REDUCTION FACTORS

422 SECTIONAL STRENGTH

423 STRUT‐AND‐TIE

424 SERVICEABILITY REQUIREMENTS

425 REINFORCEMENT DETAILS

426 CONSTRUCTION DOCUMENTS

AND INSPECTION

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Chapter 4 ‐ CONCRETE

427 STRENGTH EVALUATION OF

EXISTING STRUCTURES

428 BUILDING CODE REQUIREMENTS FOR

CONCRETE THIN SHELLS

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Chapter 4 ‐ CONCRETE

Although the changes from ACI 318‐08 to ACI 318‐11 are not as extensive or as substantive as those between ACI 318‐11 and ACI 318‐14, some of the changes in the latest cycle are definitely significant.

To reflect the reorganization of ACI 318‐14 which contained a number of significant technical changes, the ASEP

adopted similar changes in the NSCP 2015 7th _{Edition. The}

latest ACI 318 was reorganized as a member‐based

document, i. e., particular member type, such as beam, column, or slab will have separate sub‐sections for all

requirements to design that particular member type. This will eliminate the need to flip through several Sections to comply with all the necessary design requirements for a particular structural member, as was necessary with the old organization format.

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Chapter 4 ‐ CONCRETE

Section 401 — General Requirements

General information regarding the scope and applicability of NSCP 2015, Vol. 1 is provided. Additional sub‐section on

interpretation is included to help users better understand Chapter 4, Structural Concrete provisions.

Section 402: Section Notation and Terminology

The definition for hoops has been modified because the use of interlocking headed bars is a concern regarding the possibility that it will not be adequately interlocked and because the

heads could become disengaged under complex loadings well into the non‐linear range of response. It is now defined as a

closed tie or continuously wound tie, made up of one or several reinforcement elements, each having seismic hooks at both

ends. A definition for special seismic systems, a term used in Sections 418 and 419, has been added.

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Chapter 4 ‐ CONCRETE

Section 403 — Referenced Standards

The following referenced specifications have been added to Section 403.2.4:

ASTM A370‐14, Standard Test Methods and Definitions for Mechanical Testing of Steel Products

ASTM A1085‐13, Standard Specification for Cold‐Formed Welded Carbon Steel Hollow Structural Sections (HSS)

ASTM C173/C173M‐14, Standard Test Method for Air‐ Content of Freshly Mixed Concrete by Volumetric Method

ASTM C1582/C1582M‐11, Standard Specification for Admixtures to Inhibit Chloride‐Induced Corrosion of

Reinforcing Steel in Concrete

A new referenced specification from Australia and New Zealand, Section 403.2.6 is added. These standards were included as the ACI 318 has no provisions related to Qualifications on the use

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Chapter 4 ‐ CONCRETE

of Quenched Tempered QT/Thermo‐Mechanically Treated Reinforcement, which are the type manufactured, sold, and commonly used for building construction in the Philippines:

1. AS/NZS 4671: 2001, Steel Reinforcing Materials

2. NZS 3101: 2006, Part 1 and Part 2, Concrete Structures Standard, and Design of Concrete Structures

3. NZS 3109, Amendment 2, Welding of Reinforcing Steel

AS/NZS 1554.3: 2008, Part 3, Structural Steel Welding of Reinforcing Steel

The following referenced specifications have been deleted: 1. ASTM C109/C109M‐08, Standard Test Method for

Compressive Strength of Hydraulic Cement Mortars

2. ASTM C192/C192M‐07, Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory

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Chapter 4 ‐ CONCRETE

Several referenced standards and specifications have been

updated, as in most cases with every edition of the NSCP. Note that the edition of every referenced standard is important. The NSCP does not necessarily adopt new editions of referenced standards unless they are vetted before the publication of each edition of the standard.

Section 404 — Structural System Requirements

This new Section has been added to Chapter 4 to introduce structural system requirements. This Section contains Sub‐

sections on Materials, Design Loads, Structural System and Load Paths, Structural Analysis, Strength, Serviceability, Durability,

Sustainability, Structural Integrity, Fire Resistance,

Requirements for Specific Types of Construction, Construction and Inspection, and Strength Evaluation of Existing Structures.

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Chapter 4 ‐ CONCRETE

Most of these Sub‐sections refer to the other Sections in the NSCP. The Sub‐section on construction and inspection, for instance, refers to Section 426. In the areas for Sustainability and Fire Resistance, the NSCP does not have specific

requirements. This Sub‐section on Sustainability allows the licensed design professional to specify in the construction documents, sustainability requirements in addition to the strength, serviceability, and durability requirements of the

NSCP. The strength, serviceability, and durability requirements are required to take precedence over sustainability

considerations, though these requirements are generally in

harmony with sustainable structures. In the Sub‐section on Fire Resistance, the NSCP refers to the fire‐protection requirements of the NSCP Chapter 4, Sub‐section 420.6.1. However, if the

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Chapter 4 ‐ CONCRETE

National Building Code of the Philippines requires a greater concrete cover, such greater thickness shall govern.

Section 405 — Loads

The following modification has been made in the provision for live load reduction because there are still unincorporated areas where there may not be included in the previous editions of the NSCP. The 7th _{Edition, Sub‐section 405.2.3 – Live load reductions}

shall be permitted in accordance with the National Building Code of the Philippines, or in its absence, in accordance with ASCE/SEI 7.

For many Code revision cycles, ACI 318 retained provisions for service‐level earthquake forces in the design load

combinations. In 1993, ASCE/SEI 7 converted earthquake forces to strength‐level forces and reduced the earthquake load factor

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Chapter 4 ‐ CONCRETE

to 1.0, and the model building codes followed suit. In modern building codes around the world, earthquake loads are now strength‐level forces. Therefore any references to service‐level earthquake forces (as in ACI 318‐11 Sect. 9.2.1(c) have been deleted.

A requirement to include secondary moments was properly

included in earlier editions of the ACI, as in the NSCP, section on moment redistribution but was not included anywhere else.

Because secondary moments are significant considerations when a member is being designed, including when moments are not redistributed, they should be included in the member Sections. Also, the effects of reactions induced by prestressing include more than just secondary moments, so the language is modified to reflect this. Two new sub‐sections should be noted:

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Chapter 4 ‐ CONCRETE

Section 405 — Loads

405.3.11 – Required strength U shall include internal load effects due to reactions induced by prestressing with a load factor of 1.0.

407.4.1.3 – For prestressed slabs, effects of reactions induced by prestressing shall be considered in accordance with

405.3.11.

Sub‐sections 408.4.1.3 and 409.4.1.3 have, similarly, been added to the Sections on Two‐way slabs and beams,

respectively.

Section 406 — Structural Analysis

The following new item has been added in Sub‐section 406.6.2.3:

(b) For frames or continuous construction, it shall be permitted to assume the intersecting member regions are rigid.

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Chapter 4 ‐ CONCRETE

Section 406 — Structural Analysis

Previous NSCP 6th _{Edition has been silent on the use of finite}

element analysis (FEA), though it is now frequently used.

Section 406 has added 406.9 with provisions that are intended to explicitly allow the use of FEA and to provide a framework for the future expansion of FEA provisions, but not as a guide toward the selection and use of FEA software. The new Sub‐ section on diaphragms and collectors makes an explicit

reference to the use of FEA, which makes it imperative that NSCP 7th _{Edition recognize the acceptability of its use.}

Section 408 — Two‐Way Slabs

Sub‐section 418.10.1 (corresponding to ACI 318M‐11, Section 18.9.1), says that a minimum area of bonded reinforcement shall be provided in all flexural members with unbonded

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Chapter 4 ‐ CONCRETE

reinforcement over the tops of columns is to distribute cracking caused by high local flexural tensile stresses in areas of peak

negative moments. However, the high local flexural tensile stresses are not unique to slabs with unbonded tendons. The new reorganized Sub‐section 408.6.2.3 (corresponding to ACI 318M‐14 Section 8.6.2.3) requires the same minimum

reinforcement in slabs with unbonded or bonded tendons,

except that the area of bonded tendons is considered effective in controlling cracking.

It was also decided by the ACI 318 Committee, that if the same bonded reinforcement were required for both bonded and

unbonded post‐tensioned two‐way systems, the structural integrity requirements for both systems should also be the same. The structural integrity requirements in ACI 318M‐11,

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Chapter 4 ‐ CONCRETE

Section 18.12.6 applied to two‐way post‐tensioned slab systems with unbonded tendons only. The structural integrity

requirements in ACI 318M‐14 Section 8.7.5.6 (corresponding to the NSCP 2015, Sub‐section 408.7.5.6) now apply to two‐way post‐tensioned slab systems with bonded as well as unbonded tendons.

END OF PART 1:

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Chapter 4 ‐ CONCRETE

PART 2:

CHAPTER 4, STRUCTURAL CONCRETE

Section 409 — Beams

The use of open web reinforcement for torsion and shear in slender spandrel beams by the precast concrete industry as an alternative to the closed stirrups traditionally mandated by this Code. Eliminating closed stirrups is desirable because they

cause reinforcement congestion; production costs also increase significantly because pre‐tensioning strand must be threaded through the closed stirrups.

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Chapter 4 ‐ CONCRETE

An extensive PCI‐sponsored experimental and analytical research program was conducted at North Carolina State University (NCSU). The objective was to develop a rational

design procedure for slender precast concrete spandrel beams. Specifically, the research was aimed at simplifying the detailing requirements for the end regions of such beams. The end

regions are often congested with heavy reinforcement cages when designed using current procedures.

In addition to the experimental program, finite element models were developed (Fig. 2) and calibrated to experimental data. These models were used in conjunction with conventional

analysis to corroborate the experimental results and to further investigate the behavior of slender precast concrete spandrel beams.

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Chapter 4 ‐ CONCRETE

Figure 2. Finite element model of a precast concrete spandrel beam. Image from Lucier et al., “Development of a Rational Design Methodology for Precast Concrete Slender

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Chapter 4 ‐ CONCRETE

A new relevant Sub‐section 409.5.4.7 for solid precast sections is added to the NSCP 2015.

Section 412 — Diaphragms

NSCP 2015 Sub‐section 418.12 contained design and detailing requirements, for diaphragms in structures assigned in areas of high seismicity (Zone 4). For the first time, a new Section 412, added design provisions for diaphragms in buildings assigned in areas of low seismicity (Zone 2) The new Section applies “to the design of non‐prestressed and prestressed diaphragms,

including (a) through (d):

(a). Diaphragms that are cast‐in‐place slabs

(b). Diaphragms that comprise a cast‐in‐place topping slab on precast elements.

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Chapter 4 – CONCRETE

Section 412 — Diaphragms

Figure 3

(c). Diaphragms that comprise precast elements with end strips formed by either a cast‐in‐place concrete topping slab or edge beams

(d). Diaphragms of interconnected precast elements without cast‐in‐place concrete topping. (Fig. 3)

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Chapter 4 ‐ CONCRETE

Section 418 — Earthquake‐Resistant Structures

There are a number of significant and substantive changes to this Section.

Column confinement ‐ The ability of the concrete core of a

concrete reinforced column to sustain compressive strains tends to increase with confinement pressure. Compressive strains caused by axial load. It follows that confinement

reinforcement should be increased with axial load to ensure

consistent lateral deformation capacity. The dependence of the amount of required confinement on the magnitude of axial load imposed on a column has been recognized by some codes from other countries (such as CSA A23.3‐1419 and NZS 3101‐

0620,21) but was not reflected in ACI 318 through its 2011 edition.

The ability of confining steel to maintain core concrete integrity and increase deformation capacity is also related to the layout

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Chapter 4 ‐ CONCRETE

of the transverse and longitudinal reinforcement. Longitudinal reinforcement that is well distributed and laterally supported around the perimeter of a column core provides more effective confinement than a cage with larger, widely spaced longitudinal bars. Confinement effectiveness is a key parameter determining the behavior of confined concrete (Mander, et al) and has been incorporated into the CSA A23.3‐14 equation for column

confinement. ACI 318, through its 2011 edition, did not

explicitly account for confinement effectiveness in determining the required amount of confinement. It instead assumed

constant confinement effectiveness independent of how the reinforcement is distributed.

In view of this, confinement requirements for columns of

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Chapter 4 ‐ CONCRETE

axial load (P u > 0.3 A f c ', where P u is the factored axial force,

Ag is the gross area of the concrete section; and f c ‘ is the

special compressive strength of concrete) or high concrete compressive strength ( f c ' > 10,000 psi [6895 MPa]) are

significantly different in ACI 318M‐14.

One important new requirement for special moment frame columns is as follows:

418.7.5.2 — Transverse reinforcement shall be in accordance

with (a) through (f):

(f) Where P u > 0.3 A f c ‘ or f c ' > 6895 MPa in columns with

rectilinear hoops, every longitudinal bar or bundle of bars around the perimeter of the column core shall have lateral

support provided by the corner of a hoop or by a seismic hook, and the value of h x shall not exceed 200 mm. (Fig. 5). P u shall

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Chapter 4 ‐ CONCRETE

Figure 4. Confinement of rectangular column of special moment frame. Note:

h1 = plan dimension of column in one of two orthogonal directions; h2 = plan dimension

of column in other orthogonal direction; ℓo = length, measured from joint face along axis

of member, over which special transverse reinforcement must be provided; s = center‐to‐

center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors. 1 in. = 25.4 mm

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Chapter 4 ‐ CONCRETE

Figure 5. Confinement of high‐strength or highly axially loaded rectangular

column of special moment frame. Note: d b = nominal diameter of bar, wire, or

prestressing strand; h x = maximum value of x i on all column faces greater than

200 mm.; x i = dimension from centerline to centerline of laterally supported

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Chapter 4 ‐ CONCRETE

be the largest value in compression consistent with factored load combinations including E .

where:

h x = maximum center‐to‐center spacing of longitudinal bars

laterally supported by corners of crossties or hoop legs around the perimeter of the column.

The change from prior practice is that instead of every other

longitudinal bar having to be supported by a corner of a tie or a crosstie, every longitudinal bar will have to be supported when either the axial load on a column is high or the compressive

strength of the column concrete is high.

The other new requirement for special moment frame columns is in the following section:

418.7.5.4 — Amount of transverse reinforcement shall be in

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Section 418 — Earthquake‐Resistant Structures Table 418.7.5.4

Transverse Reinforcement

Conditions Applicable Expressions

  _  0.30g and Greater of (a) and (b) 0.3 g   1    (a)  70 MPa

for rectilinear hoop

  0.30g or

Greatest of (a), (b), and (c)

0.09   _ (b)  70 MPa _0.2   _ _ (c) _   0.30g and Greater of (d) and (e) 0.45 g   1    (d)  70 MPa

for spiral or circular hoop

  0.30g or Greatest of (d), (e), and (f) 0.12    (e)  70 MPa 0.35__    (f)

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Chapter 4 ‐ CONCRETE

Table 418.7.5.4 Note:

Ach = cross‐sectional area of a member measured to the outside

edges of transverse reinforcement; Ag = gross area of concrete

section; for a hollow section, Ag is the area of the concrete only and

does not include the area of the void(s); Asb = area of longitudinal

reinforcement in shear wall boundary element; bc = cross‐sectional

dimension of member core measured to the outside edges of the transverse reinforcement composing area Ash ; f c ' = specified

compressive strength of concrete; f yt = specified yield strength of

transverse reinforcement; k f = concrete strength factor;

k n = confinement effectiveness factor; P u = factored axial force, to be

taken as positive for compression and negative for tension;

s = center‐to‐center spacing of items, such as longitudinal

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Chapter 4 ‐ CONCRETE

Confinement requirements for columns of special moment

frames, and for columns not designated as part of the seismic‐ force‐resisting system in structures assigned to seismic zone 4 (similar to ASCE 7‐10 Seismic Design Categories D, E, and F), with high axial load or high concrete compressive strength are significantly different.

Transverse reinforcement ‐ One important new requirement for special moment frame columns are included in Sub‐sections

418.7.5.2 and 418.7.5.4. There are new restrictions on the use of headed reinforcement to make up hoops.

Special moment frame beam‐column joints – For beam‐column joints of special moment frames, clarification of the

development length of the beam longitudinal reinforcement

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Chapter 4 ‐ CONCRETE

reinforcement, and restrictions on joint aspect ratio are new. For beam‐column joints of special moment frames, clarification of development length of beam longitudinal reinforcement that is hooked, requirements for joints with headed longitudinal

reinforcement, and restrictions on joint aspect ratio are new. Special shear walls – Subsection 418.10 (equivalent to ACI 318‐ 14M‐14 Section 18.10, previously ACI 318M‐11 Section 21.9), has been extensively revised in view of the performance of

buildings in the Chile earthquake of 2010 and the Christchurch, New Zealand, earthquakes of 2011, as wells as full‐scale

reinforced concrete building tests. In these earthquakes and laboratory tests, concrete spalling and vertical reinforcement buckling were at times observed at wall boundaries.

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Chapter 4 ‐ CONCRETE

reinforcement in special moment frames and special shear walls, the NSCP 7th _{Edition now requires the same minimum}

elongation as ASTM A706 reinforcement.

Section 419: Concrete: Design and Durability Requirements

Quite a few changes have been made in concrete durability requirements, which are now located in this Section.

In previous editions (ACI 318‐11), section 5.1.5, says, “Splitting tensile strength tests shall not be used as a basis for field

acceptance of concrete,” and commentary section R5.1.5 have been deleted because in the latest edition (ACI 318M‐14 section 19.2.1.2) clearly says, “The specified compressive strength shall be used for mixture proportioning in 26.4.3 (NSCP 426.4.3) and for testing and acceptance of concrete in 26.12.3 (NSCP

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Chapter 4 ‐ CONCRETE

Section 420: Steel Reinforcement Properties, Durability and Embedments

The definition of yield strength of high‐strength reinforcement for Grade 420 (Grade 60) in this Section is now, for the first

time, the same as that in ASTM specifications, except for bars with less than 420 MPa, the yield strength shall be taken as the stress corresponding to a strain of 0.35 percent.

Deformed and plain stainless steel wire and welded wire conforming to ASTM A1022 is now permitted to be used as concrete reinforcement.

Sub‐section 420.2.2.5 requires “Deformed non‐prestressed

longitudinal reinforcement resisting earthquake moment, axial force, or both, in special moment frames, special structural

walls, and all the components of special structural walls including coupling beams and wall piers” to be ASTM A706

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Chapter 4 ‐ CONCRETE

Grade 420 (Grade 60), ASTM 615 Grade 275 (Grade 40) or Grade 420 (Grade 60) reinforcement is permitted if two

supplementary requirements are met, which are already part of the ASTM A706 specification. A third supplementary

requirement is now added for ASTM A615 (Grade 60)

reinforcement to be permitted for use in special moment

frames, special structural walls. The minimum elongation in 200 mm (8”) must now be the same as that ASTM A615 (Grade 60) reinforcement.

One aspect of the Code compliance that the Association of

Structural Engineers of the Philippines is cautioning Designers and Constructors alike, is the introduction of ASTM 615 Grade 520 (Grade 75) in the Philippine market. Since this was not

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Chapter 4 ‐ CONCRETE

covered by previous editions of the NSCP Vol. 1, it creates an impression of an unregulated use of a new high‐strength

reinforcement grade.

To put it clearly, Sub‐section 420.2.2.5, corresponding to ACI 318M‐14 Section 20.2.2.5, specifies the use of deformed non‐ prestressed longitudinal reinforcement resisting earthquake‐ induced moment, axial force, or both, in special moment

frames, special structural walls, and all components of special structural walls, including coupling beams, and wall piers which shall be in accordance with (a) or (b):

(a). ASTM A706M, Grade 420 (b). ASTM A615M, Grade 280

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Chapter 4 ‐ CONCRETE

allowed, although the use of micro‐alloyed high‐strength reinforcement may be allowed in the future through the

issuance of a new ASTM or updated standard, and with proper validation by the Department of Trade and Industry’s Bureau of Standards. It will be premature to allow its use for special

moment frames, special structural, and all components of special structural walls, including coupling beams, and wall piers for Buildings located in areas of high seismicity (zone 4). The same restrictions indicated in Sub‐section 420.7.6, on the use of quenched‐tempered thermo‐mechanically treated

(QT/TMT) reinforcing bars in structures located in seismic zone 4 for Grade 420 reinforcement, shall also be applied to Grade 520, unless proven in subsequent studies and tests.

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Chapter 4 ‐ CONCRETE

Section 422: Sectional Strength

The following are the changes in Section 422:

For prestressed members, a new equation for the nominal axial strength at zero eccentricity has been introduced in Sub‐section 422.4.2.3.

New Sub‐section 422.4.3.1, which requires that the nominal axial tensile strength of a non‐prestressed, composite, or

prestressed member, not to be taken greater than the maximum nominal axial tensile strength of member.

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Chapter 4 ‐ CONCRETE

Section 425: Reinforcement Details

Two changes shown in Table 7 (part of Table 425. 3.2) are made to eliminate the differences between the required tail extension of a 90‐degree or 135‐ degree standard hook, subject to a

minimum of 75 mm (3”).

Mechanical or welded splices with strengths below 125% of the yield strength of the spliced reinforcing bars are no longer

permitted. The associated stagger requirements have been deleted. Thus there is no longer a need to specify “full”

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Chapter 4 ‐ CONCRETE

Section 426: Construction Documents and Inspection

In this section, the user will probably require some time to get used to, it starts with the following:

426.1.1 This Sub‐section addresses (a) through (c):

(a) Design information that the licensed design professional shall specify in the construction documents,

(b) Compliance requirements that the licensed design professional shall specify in the construction documents,

(c) Inspection requirements that the licensed design

professional shall specify in the construction documents, Thus, construction and inspection requirements have been consolidated, and they are now related to construction

documents. The construction requirements are designated either as “design information” or “compliance requirements.” These are largely existing material that has been rearranged.

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Chapter 4 ‐ CONCRETE

The inspection requirements in Sub‐section 426.13 are taken from Chapter 17 of the 2015 International Building Code (IBC) and were previously not part of ACI 318.

Provisions in ACI 318‐11 and earlier editions, which explained basic statistical considerations in mixture proportioning, are no longer found in ACI 318‐14. Instead, ACI 301‐10, Specifications

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These are some other changes in the makeup of NSCP 2015 7th

Edition that should be noted:

1. There are two new Sections: Section 404, Structural System Requirements and Section 412, Diaphragms.

2. Section 422, Structural Plain Concrete, now Section 414.

3. Section 423, Anchoring to Concrete, is now Section 417, with no significant changes. 4. Section 421, Earthquake‐Resistant

Structures, now Section 418.

5. Section 427, Strut‐and‐Tie Models is now Section 423, with no significant changes.

6. Section 420, Strength Evaluation of Existing Structures, is now Section 427.

7. Section 419, Shells and Folded Plates, is now Section 428. 8. 8. Section 424, Alternative Design Method, now Section 429, is adapted from earlier editions of the NSCP.

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9. Section 425, Alternative Provisions for Reinforced and

Prestressed Concrete Flexural and Compression Members, and Section 426, Alternative Load and Strength Reduction Factors, have been discontinued.

10. On the other hand, Section 416, Precast Concrete, and

Section 418, Prestressed Concrete, no longer exist as separate entities. The provisions of these Sections are now spread over several of the new Sections.

Sub‐section 418.18, Requirements for post‐tensioning ducts and grouting have also been removed as being outdated. The Commentary now provides specification guidance.