Basic Design Criteria Iswandi Imran.

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1 Basic Design Criteria Iswandi Imran

2 Content Design standard and code of practice
Structural type and material Design loading: - Dead load - Live load - Time dependent load - Earthquake load - Gaya uplift - Others Load combination

3 Content (Continued) Material specification - Concrete
- Steel reinforcement - Structural steel - Others Deformation limit - Differential settlement - Structural displacement Batas toleransi pada pelaksanaan

4 Code and Design Guide AISC Codes ACI Codes SNI Codes UBC / IBC / ASCE
AASHTO Other important documents: - MCP (ACI Manual of Concrete Practice) - AISC Design Guide Dalam desain, sebaiknya menggunakan peraturan-peraturan yang konsisten satu dengan yang lainnya. Karena SNI selalu mengacu pada US code, maka sebaiknya gunakan standar-standar dari US bila ada hal-hal yang belum tercakup dalam SNI.

5 Persyaratan Struktur dan Material
Sistem struktur yang digunakan pada suatu daerah harus sesuai dengan tingkat kerawanannya terhadap gempa Aspek kontinuitas dan integritas struktur bangunan perlu diperhatikan Material yang digunakan harus memenuhi persyaratan  durabilitas Kualitas pengerjaan harus sesuai kaidah yang berlaku

6 Sistem Struktur untuk Bangunan Tahan Gempa
Penyesuaian aturan detailing dengan adanya rancangan peraturan gempa yang baru (mengacu pada UBC). Aturan detailing dibedakan berdasarkan tingkat kerawanan terhadap gempa. Sistem struktur dasar dibedakan atas: Sistem rangka pemikul momen (SRPMB,SRPMM, SRPMT & SRPMK). Sistem rangka batang pemikul momen (SRBPMK) Sistem rangka bresing konsentrik (SRBKK, SRBKB) Sistem rangka bresing eksentrik (SRBE) Sistem dinding struktural (SDSB & SDSK). Aturan detailing dapat mengacu pada SNI 2847 Pasal 23 (untuk struktur beton) dan SNI 1729 Pasal 15 (untuk struktur baja)

7 Level Resiko Gempa pada SNI 1726
SDC = Seismic Design Category SPC = Seismic Performance Category

8 SNI 2847 Pasal 23.2

9 Elemen Kunci untuk Perencanaan Struktur Tahan Gempa
Kuat Lateral Perlu SNI atau UBC 1997 atau ASCE-07: Standar Perencanaan Ketahanan Gempa untuk Struktur Bangunan Gedung Minimum Design Loads for Buildings and Other Structures Detailing untuk Daktilitas SNI Pasal 15 atau AISC Seismic Prov atau ACI 318 atau SNI Pasal 23: Tata Cara Perhitungan Struktur Baja/Beton untuk Bangunan Gedung

10 Kombinasi Beban LRFD (ASCE-7):
1.2D + 1.6L + 0.5(Lr or S or R) 1.2D + 1.6(Lr or S or R) + (0.5L or 0.8W) 1.2D + 1.6W + 0.5L + 0.5(Lr or S or R) 0.9D + 1.6W 1.2D + 1.0E + 0.5L + 0.2S 0.9D + 1.0E Load Combinations Including E

11 Kombinasi Beban Layan (ASCE-7):
1.0D 1.0D + 1.0L 1.0D + 1.0(Lr or S or R) 1.0D L (Lr or S or R) 0.6D + W 1.0D + (1.0W or 0.7E) 1.0D (W or 0.7E) L 0.6D + 0.7E Load Combinations Including E

12 Faktor Kuat Lebih f atau Ωo
Bilamana dibutuhkan perbesaran beban gempa maka komponen beban gempa horizontal E harus dikalikan dengan faktor kuat lebih o sesuai tabel.

13 Faktor Kuat Lebih f atau Ωo
Ωo Qe Lateral Seismic Force Qe As an example, the Overstrength Factor for moment frames is 3. This implies that the plastic lateral strength of a moment frame, on average, will be three times larger than the design lateral force Qe. There are typically several reasons why a frame is considerably stronger than the design lateral force. These include: - the use of resistance factors when computing design strength; - actual yield stress higher than minimum specified; - members larger than need for strength to satisfy drift limits; - members larger than needed for strength to simplify design and construction (e.g. using same size beam for several floors, even though smaller beams could be used as you move up in the building); - increase in strength in going from first plastic hinge (Qe is based on the required strength at first significant yield of the frame....i.e., first plastic hinge) to formation of a plastic mechanism. Recall from a previous slide that the maximum lateral force that a structure will see during the earthquake is defined by the structure's own lateral strength. Thus Amplified Seismic Load therefore provides an estimate of this value. Wherever the Seismic Provisions require that an element or connection must be designed for the Amplified Seismic Load, it is also permitted to conduct a plastic analysis to determine the maximum force the element will see, instead of using the Amplified Seismic Load. The Amplified Seismic Load can be viewed as a highly simplified substitute for plastic analysis. Frame Lateral Deflection Beban gempa yang diperbesar, ΩoQe, dimaksudkan untuk memberi estimasi kuat lateral plastik struktur portal.

14 Contoh Penerapan: Perhitungan Pengaruh Gempa pada Struktur Bawah
Pembebanan dari struktur atas Struktur bawah tidak boleh gagal lebih dulu dari struktur atas; Struktur bawah harus dapat memikul beban gempa maksimum Vm yang mugkin terjadi pada struktur atas  - Vm = f2 Vy - f2 = faktor kuat lebih struktur - Vm = f Vn

15 Kombinasi Beban Ultimit bila Memperhitungkan Kuat Lebih
Untuk Kombinasi: 1.2D + 1.0E + 0.5L + 0.2S Beban Gempa yang Diperbesar: E = Ωo QE Untuk Kombinasi: 0.9D + 1.0E Beban Gempa yang Diperbesar: E = Ωo QE

16 Kuat Rencana untuk Desain Struktur Beton (Pasal 11.3)
Lentur, tanpa beban aksial ………………………………………… . 0,80 Beban aksial dan beban aksial dengan lentur aksial tarik dan aksial tarik dengan lentur …..……………. 0,80 aksial tekan dan aksial tekan dengan lentur: komponen struktur dengan tulangan spiral ……... 0,70 komponen struktur lainnya ………….. 0,65 Geser dan torsi …………………………………………… ……………0,75 Tumpuan pada beton …………………………………………………..0,65 Beton polos struktural …………………………………………………..0,55

17 Faktor Reduksi Geser untuk Elemen pada SRPMK dan SDSK
Faktor reduksi untuk elemen yang kuat geser nominalnya lebih kecil dari pada gaya geser yang timbul sehubungan pengembangan kuat lentur nominalnya ……………………0,55 Faktor reduksi untuk geser pada diafragma tidak boleh melebihi faktor reduksi minimum untuk geser yang digunakan pada komponen vertikal dari sistem pemikul beban lateral. Geser pada hubungan balok-kolom dan pada balok perangkai yang diberi tulangan diagonal …………………….………………….0,80

18 Material Untuk struktur pemikul beban gempa, kuat tekan beton minimum = 20 MPa (K-250); Baja tulangan yang digunakan haruslah tulangan ulir. Baja polos hanya diperkenankan untuk tulangan spiral atau tendon; Batasan tulangan di atas tidak berlaku untuk jaring kawat baja polos.

19 Contoh Persyaratan Material (SNI 03-2847-02 Pasal 6.2)

20 Spesifikasi Baja Tulangan untuk Elemen Pemikul Beban Gempa
Untuk elemen pemikul beban gempa, baja tulangan yang disarankan adalah yang memenuhi ASTM A 706 (Paduan Rendah). Baja yang sesuai ASTM A 615 (Baja Karbon) hanya dapat digunakan bilamana: a. Mutunya dibatasi sebesar 400 MPa. b. Beberapa persyaratan lainnya juga dipenuhi:

21 Significance of “ The Overstrength Ratio” of Reinforcement
This ratio is one of the primary parameters in the capacity design procedure This ratio is used for example in design of: - shear in plastic hinge zone . - columns (“strong column weak beam”) - shear in beam-column joints. The values recommended in the design is (as an average value)

22 Significance of Yield Strength and Hardening Ratio
Excessive yield strength will cause high shear stress and high concrete bond stress when reinforcement is yielding. The length of plastic hinges formed at ends of the selected structural elements is basically influenced by the hardening ratio. The lower the ratio, the shorter is the plastic hinge length. This plastic hinge length will ultimately affect the inelastic rotational capacity and therefore, the ductility ratio of the structures.

23 Spesifikasi Baja Tulangan (ASTM A 706M, 1993)
Kuat tarik minimum, MPa 550A Kuat leleh minimum, MPa 400 Kuat leleh maksimum, MPa 540 Perpanjangan min dalam 200 mm, %: Ukuran diameter tulangan: 10, 15, dan 20 14 25, 30, dan 35 12 45 dan 55 10 AKuat tarik tidak boleh kurang dari 1.25 kali kuat leleh aktual Nilai kuat lebih maksimum batang individu = 1,35

24 Persyaratan Baja Tulangan (ASTM A 615M, 1993)
Mutu 300 Mutu 400 Mutu 500 Kuat tarik minimum, MPa 500 600 700 Kuat leleh minimum, MPa 300 400 Perpanjangan min dalam 200 mm, %: Ukuran diameter tulangan: 10 11 9 ... 15, 20 12 25 8 30 7 35, 45, 55 6

25 Spesifikasi Bahan Baja Struktural untuk Elemen Pemikul Beban Gempa
Perbandingan kuat leleh terhadap kuat tariknya adalah kurang dari 0,85, Hubungan tegangan-regangan harus memperlihatkan daerah plateau yang cukup panjang, Pengujian uniaksial tarik pada spesimen baja memperlihatkan perpanjangan maksimum tidak kurang daripada 20% untuk daerah pengukuran sepanjang 50 mm, Mempunyai sifat relatif mudah dilas.

26 Spesifikasi Bahan Baja untuk Elemen Pemikul Beban Gempa
Untuk elemen struktur yang diharapkan mengalami perilaku inelastik: Specified minimum Fy ≤ 350 MPa Pengecualian: Kolom yang diharapkan hanya leleh di bagian dasar kolom; Elemen SRPMB dan SRBKB (diijinkan menggunakan Fy hingga 385 MPa) The members of the frame that are designed to yield in an earthquake, i.e. the "fuses" in the frame (beams in moment frames, braces in SCBF and OCBF, links in EBF, etc) must be made of steel with a specified minimum yield stress of 50 ksi or less. The reason for this restriction is that the majority of experiments conducted on seismic frame elements (much of the Seismic Provisions are based on experimental research) has been on steels with a specified yield stress of 50 ksi and less (A36, A572 Gr 50, A992, A500 Gr B, etc). While elements made of higher strength steels may show satisfactory seismic performance, experimental evidence would first be needed to establish the suitability of such steels. There is reason to be cautious of higher strength steels. In general, as the strength of steel increases, its ductility decreases. That is, higher strength steels tend to be more brittle than lower strength steels. Since the key the good seismic performance is ductility, lower strength steels are, in general, preferred for yielding elements of the frame. Note that most construction materials follow this same trend. For example, higher strength concrete is generally more brittle than lower strength concrete. The requirement of Fy ≤ 50 ksi generally has little impact on design, since our common structural steels (A992, A36, etc) satisfy this requirement. There are two exceptions where higher strength steels are permitted. The first exception permits the use of higher strength steels in columns, as long as the only yielding expected in the column is at its base. In some cases, Grade 65 material can be advantageous in heavily loaded columns. The second exception permits up to Fy up to 55 ksi in yielding elements of OMFs and OCBFs. This exception is provided to accommodate materials that are commonly used in metal building systems.

27 Sifat Bahan Baja untuk Penentuan Kuat Perlu Sambungan dan Elemen Struktur Terkait
Kuat leleh yg diharapkan = Ry Fy Kuat tarik yg diharapkan = Rt Fu Fy = kuat leleh minimum yg disyaratkan Fu = kuat tarik minimum yg disyaratkan This section defines "expected yield strength," RyFy and "expected tensile strength," RtFu The concept of expected yield strength was added to the Seismic Provisions following the widespread failure of moment connections in the 1994 Northridge Earthquake. The expected yield stress recognizes that fact that the actual yield stress of steel is usually higher than the minimum specified value. For example, for A36 steel, the minimum specified yield stress is 36 ksi. However, if you run a coupon test on a piece of A36 steel, it will usually show an actual yield stress in excess on 50 ksi. In non-seismic design, having steel with an actual yield stress greater than the minimum specified value is usually not a problem. In fact, the higher yield strength provides additional reserve strength. In seismic design, however, having a higher than expected yield stress can be detrimental. We design a seismic frame so that certain elements will yield in the earthquake. These "fuses" (beams in moment frames, braces in concentrically braced frames, links in EBFs, etc) are then detailed to provide highly ductile response. However, if these fuse elements are stronger than expected, they may no longer yield in the earthquake. Instead, some other, often more brittle element, will fail before the fuse element ever yields. Consider, for example, an SMF. For this system, one of the key design requirements is that the beam-to-column connections should be stronger than the beams. That is, when the earthquake hits the frame, plastic hinges should form at the beam ends. The connections must be strong enough to permit the beam to form plastic hinges, without failure of the connection (something that did not happen in the Northridge Earthquake). For this design intent to be realized, the connections must be stronger than the actual beam, not the "theoretical" beam. Note that no matter how strong the beam is, it will still yield in the earthquake. Consequently, the moment developed at the end of the beam will reflect the actual yield stress of the beam. The expected yield stress is used to define the required strength of elements that adjoin the fuse elements in the frame, to assure that the adjoining elements are stronger than the fuse elements. For example, the beam end connections in moment frames are designed for 1.1RyFyZ . The value of RyFyZ is the plastic moment of the beam based on the expected yield stress (the expected plastic moment). The "1.1" factor accounts for additional moment generated at the end of the beam due to strain hardening of the beam. As another example of the use of expected yield stress, bracing connections in SCBF are required to be designed for an axial tension for of RyFyAg of the brace. During an earthquake, a bracing member (the fuse in an SCBF) is expected to yield in tension. In order to obtain ductile response of an SCBF, the brace must be able to yield in tension without failure of the connection. Thus, the connection is designed for an axial tension force of RyFyAg. (There is no 1.1 factor in this case, because braces exhibit little strain hardening). The expected tensile strength, RtFU is a new item added in the 2005 edition of the Seismic Provisions. The expected tensile strength is only used when checking fracture limit states in the same member for which the expected yield stress was used. This concept will be explained further with an upcoming example. Ry dan Rt adalah kuat lebih bahan yang didasarkan pada analisis statistik data mill baja.

28 Sifat Bahan Baja untuk Penentuan Kuat Perlu Sambungan dan Elemen Struktur Terkait
Berdasarkan SNI, untuk profil dan batang baja gilas (hot-rolled) Ry adalah 1,5 bila digunakan BJ 41 atau yang lebih lunak dan 1,3 bila digunakan BJ 50 atau yang lebih keras. Untuk pelat baja nilai Ry adalah 1,1. Nilai Ry lainnya dapat digunakan bila dapat didukung oleh hasil percobaan. This section defines "expected yield strength," RyFy and "expected tensile strength," RtFu The concept of expected yield strength was added to the Seismic Provisions following the widespread failure of moment connections in the 1994 Northridge Earthquake. The expected yield stress recognizes that fact that the actual yield stress of steel is usually higher than the minimum specified value. For example, for A36 steel, the minimum specified yield stress is 36 ksi. However, if you run a coupon test on a piece of A36 steel, it will usually show an actual yield stress in excess on 50 ksi. In non-seismic design, having steel with an actual yield stress greater than the minimum specified value is usually not a problem. In fact, the higher yield strength provides additional reserve strength. In seismic design, however, having a higher than expected yield stress can be detrimental. We design a seismic frame so that certain elements will yield in the earthquake. These "fuses" (beams in moment frames, braces in concentrically braced frames, links in EBFs, etc) are then detailed to provide highly ductile response. However, if these fuse elements are stronger than expected, they may no longer yield in the earthquake. Instead, some other, often more brittle element, will fail before the fuse element ever yields. Consider, for example, an SMF. For this system, one of the key design requirements is that the beam-to-column connections should be stronger than the beams. That is, when the earthquake hits the frame, plastic hinges should form at the beam ends. The connections must be strong enough to permit the beam to form plastic hinges, without failure of the connection (something that did not happen in the Northridge Earthquake). For this design intent to be realized, the connections must be stronger than the actual beam, not the "theoretical" beam. Note that no matter how strong the beam is, it will still yield in the earthquake. Consequently, the moment developed at the end of the beam will reflect the actual yield stress of the beam. The expected yield stress is used to define the required strength of elements that adjoin the fuse elements in the frame, to assure that the adjoining elements are stronger than the fuse elements. For example, the beam end connections in moment frames are designed for 1.1RyFyZ . The value of RyFyZ is the plastic moment of the beam based on the expected yield stress (the expected plastic moment). The "1.1" factor accounts for additional moment generated at the end of the beam due to strain hardening of the beam. As another example of the use of expected yield stress, bracing connections in SCBF are required to be designed for an axial tension for of RyFyAg of the brace. During an earthquake, a bracing member (the fuse in an SCBF) is expected to yield in tension. In order to obtain ductile response of an SCBF, the brace must be able to yield in tension without failure of the connection. Thus, the connection is designed for an axial tension force of RyFyAg. (There is no 1.1 factor in this case, because braces exhibit little strain hardening). The expected tensile strength, RtFU is a new item added in the 2005 edition of the Seismic Provisions. The expected tensile strength is only used when checking fracture limit states in the same member for which the expected yield stress was used. This concept will be explained further with an upcoming example.

29 Contoh nilai Ry dan Rt Berdasarkan AISC’05 untuk Berbagai Jenis Elemen Baja
Aplikasi Penampang Hot-Rolled dan Bar: ASTM A ASTM A572 Gr ASTM A992; A572 Gr 50 or Gr 55; ASTM A913 Gr 50, 60 or 65; ASTM A588; A1011 HSLAS Gr ASTM A529 Gr ASTM A529 Gr Penampang Berongga (Hollow Structural Sections): ASTM A500 Gr B or Gr C; ASTM A Pipa: ASTM A Pelat: ASTM A ASTM A572 Gr50; ASTM A Table I-6-1 in the Seismic Provisions specify values of Ry and Rt. These values are based on statistical analysis of mill test report data.

30 Example of Deflection Limit (IBC Table 1604.4)

31 Settlement Criteria TPKB: - max settlement = 10 cm
- diff settlement = L/300 - lendutan dikepala tiang akibat beban lateral=1,27 cm Koerner (Constr and Geotechnical Method in Engineering): - Cracking of Non-structural elem = L/300 - Structural strength reduction = L/150 - Function impaired = L/50

32 Batas Toleransi Eksentrisitas kolom  5%-10% dimensi
Eksentrisitas tiang pancang Kelurusan kolom Kelurusan girder  L/1000 (3mm in 3m) Dan lain-lain

33 Contoh Koefisien Friksi
Elastomeric to steel/concrete = 0.7 Concrete to concrete = TFE to TFE =0.05 Steel to grout = 0.55 Dan lain-lain

34 Koefisien Friksi Minimum Berdasarkan BS-5975:1996